Lenny and Carl, to the point of it being lampshaded.
Lenny: I can't tell where Carl ends and I begin!
Carl: See, comments like those are why people think we're gay.
Lenny: Even Bart was throwing dough around. He paid me and Carl a thousand bucks to kiss each other.
Carl: Hey, did we ever get that money?
- The writers enjoy hinting it such as when the pair were watching Homer and Marge kiss: "Carl remember when we used to kiss like that (beat) with our respective girlfriends?" and also when Homer is organising gay weddings but has run out of clients we get this Crowning Moment of Funny:
Bart: All you can do now is wait for some straight guys to turn.
Homer: Hmm, where are Lenny and Carl?
Marge: Don't you rush those two! That is something they need to work out themselves.