The Comic is not Relieved
There are lots of ways to provide comic relief in a story. My personal favorite, of course, is the sarcastic cynic who can never bring him/herself to take anything seriously. Unfortunately, since they're my favorite in general, I dote on their backstory until they have enough depth to make them more than the comic relief. They now have complicated emotional problems that, because they show so little genuine emotion, come out erratically in big fiery balls of angst. Mind you, these characters are usually pretty hard on the angst-ridden protagonists that they inevitably come along with, so this is kind of a conflict of interest.
The easy solution to this is to have the cynic treat the angst burst with the same disdain, sarcasm, and unconcern that they do the angst bursts of the protagonist. This works to bring the cynic closer to the protagonist, without losing the appeal of comic relief. You also don't have to lose the character development, just stick it in at relevant points in time.
See? Writing is fun!
