Rod and Nicky in Avenue Q are this way too. From the song "It Sucks to be Me":
Rod: We live together -
Nicky: We're close as people can get.
Rod: We've been the best of buddies,
Nicky: Ever since the day we met.
Rod: So he knows lots of ways to make me really upset!
Rod: Oh, every day is an aggravation -
Nicky: Come on, that's an exaggeration!
Rod: You leave your clothes out, you put your feet on my chair.
Nicky: Oh yeah? You do such anal things like ironing your underwear!
Rod: You make the very small apartment we share a Hell!
Nicky: So do you! That's why I'm in Hell too!
The Earls of Tolloller and Mountararat from Gilbert and Sullivan's Opera Iolanthe are this - there's an entire scene which hinges on Mountararat tricking Tolloller into insulting himself, but they're still very fond of each other, as evidenced in the scene where they try to decide which one of them is to marry Phyllis. (It's worth noting that this scene is also one of the most Ho Yay-laden scenes in the entire G&S canon, ending with the two men deciding that they like each-other too much to fight over her or marry her at all.
- By the end of the play, Nicky finds Rod a boyfriend to make up for outing him at Brian and Christmas Eve's wedding.
Phyllis: How can [whether she marries Tolloller or Mountararat] possibly concern me? You are both Earls, and you are both rich, and you are both plain.
Mountararat: So we are. At least I am.
Tolloller: So am I.
Mountararat: No, no!
Tolloller: Oh, I am indeed very plain.
Mountararat: Well, well! Perhaps you are.
Phyllis: There's really nothing to choose between you. If one of you would forego his title and distribute his estates amongst his Irish tenantry, why, then I should see a reason for accepting the other. (Phyllis retires up.)
Mountararat: Tolloller, are you prepared to make this sacrifice?
Mountararat: Not even to oblige a lady?
Tolloller: No! Not even to oblige a lady.
Mountararat: Then the only question is, which of us shall give way to the other? Perhaps, upon the whole, she would be happier with me. I don't know; I may be wrong.
Tolloller: No, I don't know that you are. I really believe that she would. But the awkward part of the thing is, that if you rob me of the girl of my heart, we must fight and one of us must die. It's a family tradition that I have sworn to respect. It's a painful position, for I have a very strong regard for you, George.
Mountararat: (much affected) My dear Thomas!
Tolloller: You are very dear to me, George. We were boys together - or at least I was. If I were to survive you, my existence would be hopelessly embittered.