The ever-inseparable Sam and Max have had quite a few instances of this, in particular Max who "doesn't like girls". He prefers violence.
And, true to the fact that all Ho Yay is where you find it, Max is always surprised to be told this.
Telltale pokes fun at this sometimes, like when Sybil Pandemik ran a dating service and told Sam his soulmate was Max, as well as a few possible jokes you can get using the wedding cake and engagement ring on Max, with Sam thinking over proposing to Max in his head, before giving his characteristic "Nah".
Although, in Sybil's position, wouldn't you do everything you could to keep either of them from breeding?
In one episode, Sam and Max raise a baby alligator like a couple. If it means anything, Sam is a frequent crossdresser.
In Little Bigfoot, Max was in Sam's pants. It almost makes a little bit more sense in context, but not much.
They even have a "break-up" mini-episode in there.
And to top it all off:
"You know, at moments like these, Sam and I have a special way of showing how we feel about one another"
Another episode (which was Valentine's Day themed), they had to chase their targets into a carnival that was "Couples Only". Max had to go undercover dressed in a dress, wig, make-up, and high heels. Max doesn't even complain or object, and Sam even corrects himself by saying, "Hang on, Max! I mean Sweetie!"
Also the duo's aversion to the opposite sex. The ships practically write themselves to the point where I'm not even sure that this qualifies as Heterosexual Life-Partners anymore.
In "Moai Better Blues," you see the following conversation when you examine the punching bag.
Sam: I'd hoped that after getting a punching bag for the office, Max would stop hitting me all the time.
Max: But that's how I show affection!
Sam: Well could you stop loving me so much before 6AM?
Max: No way, Sam! I could never stop loving you!
In The Glazed McGuffin Affair, when Sam slaps a hysterical Max to calm him down, he responds by saying "Hit me again. I like it!" This would be a weird thing to say, even for Max, but if he actually sees violence as a form of affection, then he might just like that Sam's being "affectionate" with him.
The Bachelor party in What's New Beelzebub? For once the duo's reaction mirrored the player's exactly.
Also, from What's New Beelzebub?, Sam's comment about Sexy Demon Peepers:
Sam: I hate to admit it, but Peepers is kinda sexy.
Max: If you're into small guys with annoying voices, I guess.
A Crowning Moment of Ho Yay: Harry Moleman frisking Sam in "Bright Side of the Moon".
In "The Penal Zone", if Max is with you when you pick up the ring, he will confuse the situation for a proposal.
Max: Sam, this is all so sudden. I don't know what to say.
If you use the Ring with Max outside Mamma Bosco's Lab, you get a whole cutscene, parodying DeBeers Commercials, in which Sam thinks about actually giving the ring to Max, but eventually discards this with a 'nah'.
The mere fact that Sam actually seems to seriously consider it says it all.
Max apparently has a habit of coming up with creepy disaster scenarios that end with him eating Sam to survive. Sam is annoyed by this, so Max tells him to just "stop looking so damn tasty."
Also a Crowning Moment of Funny, "Beyond the Alley of the Dolls" has a potential future for Sam as a reenactment of the death scene from Romeo and Juliet. Max is Juliet.
As for other characters, there's the way Skun-ka'pe and Papierwaite's relationship is discussed. While their brief cooperation itself doesn't merit raising of eyebrows, everyone involved refers to the end of said cooperation as "dumping", and the two even disagree on which one of them did the dumping.
In the dress-up Mini-Game, possible costumes for the guys include wedding clothes (Sam as the groom and Max as the bride).
If you attempt to ride the Tunnel of Love while Max is trapped in the tank, Sam will refuse, saying it 'wouldn't be romantic without Max'.
In "Hit the Road", the player attempting to grab or pick up any character other than Max will have Sam saying "He/She's not my type". Attempting to use the ropes on Max earns this suggestive bit of dialogue:
Later on they leave her alone on a raft in middle of the ocean, as Max assures her that she'll get picked up by sailors.
The Crazy part is especially apparent when Peepers takes Max's place in Sam's personal hell.Crazy Jealous Guy indeed.
It's always Sam who has to remind Max that he doesn't like girls- and that happens any time Max shows apparent interest in girls. The one time it wasn't Sam, it was Skun-ka'pe's computer. Apparently time-travelling to their childhood in Chariots of the Dogs did nothing to actually turn Max straight. It just made him more obnoxious!
"Moai Better Blues" has Max begging Sam to take baby Jimmy Hoffa home with them. When Sam responds with "Not now, Max", Max proceeds to ask "Then when?" and goes on to say that his biological clock is ticking and he's not getting any younger.