Both parodied and subverted in Scott Pilgrim via Scott's roommate Wallace. We initially learn that Wallace is gay not because of his actions, but rather because no-one will shut up about it to the point where it becomes blatantly superfluous. Later we do actually see Wallace in relationships with men, however it's often intentionally exaggerated to draw attention to itself (especially so in The Movie).
The only reason anyone knows that Northstar from Alpha Flight and the X-Men is gay is because he can't seem to go five minutes without referencing that fact. Less so that now he actually has a steady boyfriend and in fact married him in a high profile event, but in the days right after he came out, it seemed like he couldn't stop coming out.
Wiccan and Hulkling of the Young Avengers tend to go out of their way to remind people of the fact that they're dating
Averted in Gillen's run - we actually get to see more of their relationship and what they're like by themselves, so they're not just paying lipservice to it anymore.
Damian from Mean Girls being "almost too gay to function" doesn't seem to involve him dating or even being attracted to men. Although to some extent this can be Truth in Television for gay teens in high school (the not-dating part) as there are often few openly gay kids around.
In The House of Night, Damien is kind of like this, until he gets a boyfriend (so there at least is an excuse to mention that he is gay).
In Otherland, Susan van Bleeck's butler, Jeremiah Dako, is openly gay but, due to the circumstances of his employment and later, his involvement with the protagonists' quest, he is never shown having a relationship. He laments this in character, subtly lampshading the trope.
In Cell, one of the characters randomly reveals he is gay for one line. It is never brought up again.
Live Action TV
Will and Grace spent a while getting Will a boyfriend while securing Grace as his soul mate. A prominent episode in the first season being one where Grace has a boring romance in the typical manner with some guy in Story A, with Story B focusing on Will talking on the phone to some guy that he liked, in an unnecessary, one-episode version of He Who Must Not Be Seen.
Not to mention Jack, most of the time. Sure, he's sometimes seen with a date, but mostly he's seen talking about being on or going on a date.
Eric Van Der Woodsen from Gossip Girl might also fit this. One episode featured his "outing" in it's A-story, yet to date he never seems to be closer than 8 inches to his "boyfriend". If you were to watch the show muted, you would probably just guess they were just friends.
Serena Southerlyn from Law & Order. Less so than most in that the show doesn't really show any of the main characters romances.
George Huang from SVU as well. He's mentioned twice that he is gay and has never had even a mention of a relationship.
Jody, Billy Crystal's character in Soap, verbally informed the audience of his sexual preference pretty much every episode, yet you saw him going out with women far more often than with other guys. This was because the show's producers and ABC's standards and practices department had to walk on eggshells with regards to their treatment of Jody. A few years earlier, NBC had canceled the sitcom Snip less than a month before its pilot episode's scheduled debut — it didn't even get the chance to be a One-Episode Wonder — because of the public backlash over what would have been the first open gay character on an American TV series.
Jody at least had an excuse: his family members were deep in denial. A typical exchange would go something like:
Danny: Let's go out and hook up with some girls.
Jody: Danny, I don't want to do that, I'm gay.
Danny: No, 'cause you're my brother, and my brother is not gay! You're just shy.
Queer as Folk, strangely enough. Vic is undoubtedly gay, but is portrayed as almost asexual for a long time.
Partly Truth in Television, as it can sometimes be much harder for older gay men — especially ones who are HIV+, as Vic was — to find the same sort of sexual and romantic opportunities that their younger counterparts have.
During the first season of QI, Stephen Fry pointed out quite often that he's into man on man action, while the panelists rarely commented on this. The later seasons have developed into a general parade of Ho Yay, with many of the panelists openly flirting with Fry. As a rule of thumb, the later in the show a particular episode is, the more homoeroticism will be present.
Britannia High had Jez, in which his father mentions him being gay and Jez confirms it later on. There's also when a guy who likes Jez tells Lola, one of Jez's friends to ask him out for him, in which she does, but Jez thinks she's pointing to an ugly guy stood next to the other guy, who both have similar shirts. Hilarity Ensues. However, this is never mentioned again and Jez does not get a boyfriend/kiss/hug/love interest at all. Instead, he gets a kiss from a girl.
Glee: The first few episodes spend time reinforcing the fact that Kurt Hummel is gay - his crush on classmate Finn is a plot point during the first season - and yet the boy doesn't get a kiss until season two. After that, he gets boyfriend Blaine and they share varying degrees of physical affection throughout the rest of the series. This is of course Truth in Television seeing as they lived in homophobic small town Ohio and the odds of finding love when you're the only out gay kid at your school is pretty slim.
In Living Color! had a sketch in which a gay man (played by Jim Carrey) would just randomly go up to people and say "Hi. I'm gay."
Played with, in that his isolation from other gay people is entirely self-imposed due to his blind spot about being "the only gay in the village", which causes him to reject the (many, many) other gay people in the village as not being gay even when he is set up on a date, or has the opportunity to join a gay social group, or learns that he's not even the only gay person in his own family.
They make good on his sexuality in season two, with an episode taking place at a gay club, and showing Danny lamenting his breakup as his ex dances nearby. And of course, there's a funny bit were Scott is using Super Senses to try and find a werewolf, sniffs Danny who helpfully pipes up he's wearing Armani.
Season 3 features a fairly explicit scene with Danny and Ethan in a motel room. There are also two boys making out in the background at Lydia's party in season two, and one of them appears to be Danny at first glance but isn't.
He got better. Still playing the trope straight (ahem) throughout season 4.
Top Chef features at least one openly homosexual contestant in almost every season. Many of them make sure everybody knows their orientation as soon as possible. Ash in Season 6 states that he's the only chef "with a boyfriend," and then pauses for a second before elaborating, "a same-sex boyfriend."
Most of the cast of Queer Duck suffers from this.
Utahraptor from Dinosaur Comics, but that has more to do with the medium - the visual part of the comic is the same in every strip, so there's no space for, say, a strip. In the words of the author, "He is gay, guys. Only he doesn't talk about it all the time, on account of having interests outside of being gay?"
Reporter: (after the video link with another reporter cuts out due to zombies) OH GOD! We lost the video! I'm still gay, but we don't know where Dave is!
There was a Very Special Episode of The Simpsons guest starring John Waters that revolved around homosexuality. Though the Waters character was undeniably flamboyant, one awkward conversation with Smithers aside, he never actually shows his sexual preference.
In the "Honey Pot" episode of Archer, Sterling Archer attempts to seduce a gay man by posing as a ridiculous stereotype of one: he dyes his hair blond and wears roller skates, skin-tight short shorts, and a shirt that says "Got Dick?"
Doesn't really fit this trope, as Sterling isn't actually gay. Ray Gillette, conversely, does fit this trope as his sexuality is frequently mentioned but never really demonstrated.
Stewie Griffin of Family Guy is constantly hinted as being gay but it's never amounted to anything, which is a bit suspicious considering the amount of girls he's been with or crushed on.
Terry and Greg from American Dad! apply to this; though their relationship has driven the plot several times and they are common characters, the most intimate they get is holding hands and the occasional innuendo. Even lampshaded in Don't Look a Smith Horse in the Mouth, which supplies the quote at the top of the article.