I feel like that's dependant on the friend, company, and situation. I had a friend in highschool nicknamed cheddar, and it was sort of a running joke for us to call eachother couple's nicknames. our cirlce of friends were all fine with it, and even my fiance (now husband) thought it was fun, but outsiders who didn't understand our relationship were often very uncomfortable seeming to get the idea that we could be in a poliamorous lesbian relationship, which caused our families some confusion seeing how all, but maybe 1 or 2 of us were straight, and I was engaged to a man XD
Personally I think it's perfectly fine to refer to a friend that way regardless, but not everyone is comfortable with it. fortunately, it's not something people make a big stink out of anymore. a few hundred years ago we probably would have nearly been stoned to death for even discussing it. lol