The Gold Standard
** Fuck. In all its wonderful variations. Frequently heard as "Fuuuuuuuuuck."
Slightly More Creative
** Fuckbomb (thanks, elizabethf!)
Much More Creative
These are primarily thanks to ariedana, who once distracted me from an emotionally volatile situation by inviting me to come up with some truly creative insults.
** Shit-snorting sphincter
** Piss-gargling prag
Ummm... there were more but I can't remember them.