A word that just rolls out of your mouth when you're extremly pissed and try calling someone a cocksucker but by the time you're half-way into the word your anger has escalated so much that all you wanna say is '
fuck'.
Also can happen if you've been using '
fuck' so many times that your brain doesn't have the time to override '
fuck' with the next syllable of the word you're trying to say.