a chucklehead is someone who is annoying, stupid/idiotic, lame and is a huge prick!
leith: gosh! today while i was studying, joel brendans threw fruit nuggets at my head!
jeffery: zomg what chuckleheads! gosh!
Generally, a clueless weirdo who is incredibly silly (can have other general meanings).
Diana: that's so pants!
Diana: zomgosh you're such a nong!