Included in this crowd are a dog, a zombie construct, and at least one lesbian.
Yes, yes, we all know Girl on Girl Is Hot. But what some authors are only just beginning to realize is that, for a growing number of women (and of course, certainguys) Guy On Guy Is Hot. While not a ubiquitous cultural assumption in Real Life the way its Sister Trope is, it is nevertheless an existing mentality. It's the reason for the Boys Love Genre, and the times when Ho Yay is played intentionally for Fetish Fuel. Some authors adhere to this, or at least acknowledge its existence, and thus we get scenes of naked and half-naked menwrestling in either mud or jello.
In fiction, this philosophy may be treated in-universe as a full-on Spear Counterpart to Girl on Girl Is Hot, with the assumption being that it's normal for women to ogle gay men in the same way that straight men (supposedly) enjoy lesbian action.
Just as often, though, there is a heavy Double Standard; straight men thinking Girl on Girl Is Hot will be taken for granted, whereas the female enjoyment of Guy-on-Guy will be treated as a perversion (See Yaoi Fangirl). Or, in the other direction, female characters will proudly declare their fascination with gay guys doing it while denouncing men who eroticise lesbians as exploitative perverts.
In Naruto, Konohamaru's Sexy No Jutsu had two shadow clones transform into a nude Sasuke and Sai locked in a very suggestive pose. It got cut in the anime, but the manga version can be seen here. In the English print of this manga scene, the male on male part was nearly blacked out entirely, while the girl on girl scene only needed a few extra clouds to censor naughty bits. Major Double Standard on VIZ's part. Remember kids; getting the hots for naked ladies together is okay, but you're not allowed to even look at two guys. EVER!
Ohno and Ogiue from Genshiken love their yaoi, although the latter is loath to admit it at first.
This trope is a large part of Axis Powers Hetalia's raison d'être. France spends most of his time stripping and/or groping the other male characters, Italy has a habit of glomping or sleeping with Germany while naked, and the series even has its own resident Yaoi Fangirl, Hungary.
For once played for drama in Ooku. When Shogun Tsunayoshi is developing God Save Us from the Queen tendencies, she orders two of her male concubines to have sex for her entertainment, thinking they won't mind since she knows them to be lovers. They're so insulted at being used for voyeuristic thrills that they commit seppuku, giving her a salutory shock.
In The Princess Diaries 2 (which is a Disney movie aimed at pre-teen girls, just so we're clear), there is a scene where Mia and her best friend Lilly are looking at prospective princes. Mia remarks that one prince shown is cute, to which her bodyguard Joseph replies, "His boyfriend thinks so too." Mia and Lilly's reaction is... enthusiastic.
Mia and Lilly: [punch the air] Right on!
In Get Smart, when Max appears to be humping a male Control agent (he's actually trying to pull him off the table), a guard, in a rare male example, walks by and looks a little too interested before being pulled away.
In The Pink Panther Strikes Again, when Clouseau is attempting to revive Dreyfus at the insane asylum (from behind), two women mistake him for attempting to make out with him. The older one snaps, "Don't look, Fiona!" but Fiona, the younger one, seems pretty eager to watch what she thinks is two guys going at it.
Anita Blake. Two guys together gets Anita and Belle Morte off.
There was an episode of Sex and the City where the girls rent gay porn for this reason and watch it together.
Buffy the Vampire Slayer gets annoyed with the mutual jealousy of her two vampire ex-boyfriends and suggests putting them in a room together and having them wrestle it out. When Spike says it's fine with him, her eyes widen with excitement and she adds, "There could be oil involved." Note that this trope is a view held by much of the show's fanbase as well.
There was a skit on The Chris Rock Show where two men cross paths on the street and it looks like they're about to fight... and they make out instead. All you can hear from the audience is women squeeing. You can watch it here (even if the end was just spoiled out of necessity). While hilarious, the clip is sadly a case of artistic license, as racial bias and tension have long been a sore point in the gay community.
State of Play. A homosexual member of the newsroom mentions he just slept with the man they've been investigating. When he asks if they want him to go into detail the men immediately say "No!" while the female journalists have exactly the opposite response.
In one Friends episode, Rachel had an Erotic Dream that featured Chandler. Later, it also included Joey, then Rachel mentions that sometimes it was just Chandler and Joey. The guys leer until they realise what that means.
Saturday Night Live has a recurring skit called the "Kissing Family" which features a considerable amount of intense guy-on-guy kissing. Inevitably there will be squeals of delight which overpower the laughter.
Jack: We'll have a steak, watch a movie... you like gay porn, right? Grace: Who doesn't?
Noah's Arc: Brandy finds two guys together quite sexy, though overall the trope goes without saying for the LGBT genre (at least on the male end).
In the Farscape episode "Won't Get Fooled Again", one of the many crazy scenes involves a Camp Gay D'Argo propositioning John. Apparently Chiana wants to watch...
One of the Patients of the Week on Grey's Anatomy was a gay soldier. Once his boyfriend comes to visit him they are alone and proceed to make out. Meredith Grey walks by, and stares at them with much interest.
Doctor Who, "The Doctor's Daughter" - Jenny kisses a guard through the cell bars so she can grab his gun.
Donna: (to the Doctor) I'd like to see you try that.
Take That used to do lots of Ho Yay moments that extended to naked pics in their early days as well, but they stopped because they want a wider audience. Needless to say, many of their female and gay male fans left.
The Peaches song, "Two Guys (For Every Girl)" is about Peaches wanting to see her men have sex with each other.
In Shadow Hearts: Covenant, after you beat The Great Gama in Joachim's sidequest, he passes on his abilities to Joachim by engaging in some off-screen gay sex with him in the wrestling ring right in front of the whole party. While Juri isn't especially thrilled to see this, Anastasia comments that she finds it "beautiful".
In order to force Ethan to get together with a guy who previously called him out on his jerkish behaviour, Robin adds a clause to the anti-cancer bill she's trying to get through Congress that will force the two to make out at least once a week. As soon as she does, the bill gains significant support among women.
Amber repeatedly expresses enthusiasm for anything which results in two dudes getting it on.