I once read a manga where, in order to ward off an annoying girl, a guy pretends to be his friend's girlfriend, and then they both realize they like each other, or something like that. I've been looking for it for awhile, but I can't seem to find it. Anyone have any idea what it might be?

Also, I would like suggestions of similar type situations of pretend-relationships, particularly where one guy pretends to be the other's girlfriend, but just pretending to be boyfriends is fine, too. I don't care if it's smut or fluff; I'll take either.

Beep beep, all aboard the idiot wagon.

Neither is the story you are seeking, but
Fine Play by Kano Shiuko and
Iberiko Buta by Shoowa
both contain the "camouflage boyfriend" element.

You also might be able to find a few other relevant titles here and here!