1) A bumbling, stupid, inept person.
2) A confusing mess; a conundrum; any chaotic situation
3) A person of low intelligence who gets himself into a comical quandary.
"Frank just took off for the store and forgot his wallet again. What a chucklefuck!"
"When the storm hit in the middle of the parade, the whole festival became one big chucklefuck."
"That chucklefuck Frank got drunk and drank from that shampoo bottle."
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.