When a character, usually a male one, ends up enacting, complimenting, or acknowledging another man's sexuality. A split second later he will become alarmed at how incredibly gay they sounded just then, and will make a special Have I Mentioned I Am Heterosexual Today? effort in order to re-affirm how he is totally not gay. Some consider this offensive to homosexuals since, after all, there's not supposed to be anything wrong with that.
The main hallmark of this trope is that it's a deliberate act with a non-sexual instigator, though often an unconscious one which only becomes "gay" when the character looks back and realize what he sounded like. Contrast Stupid Sexy Flanders, which does have a sexual instigator.
This trope is oddly less common with women, where such compliments can exist without implying that the speaker is a lesbian—even though she may still be amiable to Three-Way Sex later.
See also Accidental Hug, Accidental Kiss, That Came Out Wrong. Compare & contrast Gay Bravado, where a straight guy uses this kind of thing specifically to affirm his heterosexuality.
ThisSuper Bowlad has a couple of men have an Accidental Kiss while eating a Snickers bar. They are so overcome with alarm that they immediately try to do the manliest things they can think of to shrug it off. Led to Unfortunate Implications when several of the "vote for the ending!" endings featured on the site involved violence... along side several videos of pro football players watching the ad and going, "Ewwww."
In one Zits strip, Jeremy and Hector are very close to engaging in a brohug, before glancing awkwardly at each other and saying TV makes it look a lot easier. Jeremy then says "Let Us Never Speak of This Again".
In The Eclipse of the Century (a YA novel by Jan Mark), in an episode of stress-fueled slightly hysterical silliness, the main character and another man end up embracing while dressed in women's clothing. They then both confirm that they're not gay.
A stronger, because more mutual, example, occurs in another episode when Al happens to graze Jefferson's hand when they're sitting next to each other on the couch.
Al: Jefferson, your skin is so soft.
Jefferson: Oh, Al, you say the nicest things.
Al: Well, it's easy when I'm with you.
They gaze into each others' eyes for a moment; then they catch themselves and start talking, in a much lower register, about the Chicago Bears' prospects for the season.
Earlier, between Al and Steve when they're mistaken for a gay couple:
Al: If I was gay, I'd like to think I could do better than him.
Steve: What's that supposed to mean?
Al: You don't turn me on! Yeah, I said it!
On Friends, Chandler tells Ross, "I'd miss you if I broke up with you." Ross asks why he said that, and Chandler says he's just trying to be supportive. Ross says, "Well, be supportive like a guy."
Joey and Chandler have a ton of these over the course of the series, including the time Chandler asks "hey, do we hug too much?" and the episodes in which Joey's decision to move out of their apartment was jokingly played like a romantic breakup. Ross and Joey also have one in "The One With the Nap Partners," for obvious reasons. Chandler even sort of has one with his father-in-law Jack when he accidentally sits on his lap in a really steamy steam room...while they're both naked.
While J.D. and Turk in Scrubs usually don't care about showing their love for each other, there is one episode where J.D. makes mention to one time where Elliot's boyfriend got drunk and accidentally climbed into his bed instead of her's, gave JD a kiss on the cheek and said "Hello, lover" while putting his arms around him. The mostly asleep JD responded with "Mmmm... tender." Back to the present, JD is explaining to Turk that anyone who woke up that way would let out a pleasure moan no matter who the other person was (plus Keith was "a decent kisser"). Then Turk recalls a similar incident in college, and JD says something like "Who drunkenly climbed into your bed and kissed you?" Suddenly both their expressions change to mild horror as JD's voice over says something about them having repressed that memory for years and they quietly agree not to hang out for a couple of weeks.
There's also the subversion with the "Guy Love" song in My Musical.
It's played straight when JD sings the line "He's the only man who's ever been inside of me!" Turk immediately clarifies that he just took out JD's appendix. Apparently, the rest of the song was just fine, though.
"And when I say I love you Turk/It's not what it implies ..."
Both of these double as a Crowning Moment of Funny. It should also be pointed out that the JD/Turk thing is a Running Gag, to the point where even Carla grumbles that JD is her husband's first love.
And then there's that one time JD goes to imagine him and Turk having sex (Elliot prompted him) . . . only for the fantasy to consist of Turk putting his hand on top of JD's to sexy music.
Just a few more quotes:
JD: "I'm having a really gay day."
Turk: "How come you don't point it out when I ask good questions?"
Carla: "Because I don't love you like he does."
JD: (singsongedly)"Told you."
JD: "I don't have gay Jungle Fever!"
Happens occasionally on How I Met Your Mother, such as when Ted describes to Barney (through song) his plans for an amazing 'Super Date'. By the end of the song, both Barney and Ted are noticeably caught up in all of the romance, and go to a strip club to shake it off.
Not to mention the episode where Barney and Marshall spend all day pretending to be a girl (through text) to make Ted fall in love with them and then end up arguing over which of them Ted would most likely be in love with.
Buffy the Vampire Slayer - Xander is in a struggle with knife-wielding class psycho Jack - a policeman shows up and asks what's going on; Xander tells him "Nothing! - just blowing off steam. Two guys rasslin'...but not in a gay way!"
One memorable moment on QI has Rob Brydon and Ben Miller kissing each other on the lips in response to all the teasing from the panel about how similar they look, before declaring, "Now I know why my wife married me!" and "That's what it's like! I can see the attraction!" respectively.
In the musical Thirteen two characters go to kiss the same girl, she moves suddenly, they kiss each other... and there's an awkward moment before they turn away. Depending on the version you see, they act manly afterward, to counteract the kiss.
In the Yu-Gi-Oh Abridged Movie Yusei and the Pharaoh seem to find each other equally cool (And Jaden equally sucky) and keep complimenting each other before with Careless Whisper playing in the background before breaking it up with "No homo". Subverted at the end when Yusei asks "No homo, right?" and the Pharaoh replies with "ALL OF THE HOMO"!
In season 3, Riley adds "No homo" when he says anything that might be considered gay. He adds "Pause" to give others (mostly Granddad) a chance to add "no homo" to save themselves from being Mistaken for Gay before he mocks them.