Crackfic is . . . perhaps an acquired taste. It's hard to define, other than to say that it's usually giddy and self-conscious in tone. It plays with fanon stereotypes and often deliberately breaks the rules in terms of genre and characterization. It's silly, and fun to write.
It's certainly not everyone's cup of tea. But if you like crackfics, check out some of these Snape/Harry gems.