Oh, damn, I just heard myself murmur distractedly, “Just let me align my waterfowl …” before beginning my next presentation.
I admit I find words like ‘misbegotten’, ‘diseased’, and ‘cretin’ more satisfying than ‘stupid rotten bastard’, but I think we are being a bit too clever here.
How about mother-fucking cock-sucking two-balled bitch for some simple dirty trash?
I like punchy, two-part words - like Knobjockey or Shagsack
What’s wrong with fucktard, fucktard? 
You people are so fucking picky. DAMN!
I’ve never had the opportunity to use it, so you can have coprophageous microcephaloid if you like. It’s a bit pretentious, but it’s fun.
I picked up the phrase “misbegotten son of a wombat” somewhere. I’m holding it in reserve against some Aussie causing me the right degree of amused outrage to use it.
As for “too clever”, I present an excessively erudite exclamation I constructed on a dare, many years ago:
“Attempt aerial coitus with a continuously axially reoriented and linearly displaced toroidal pastry.”
While playing Loaded Questions with friends, a category along the lines of “What’s the worst name you can call someone?” came up. My friends asked how many hyphenated words were allowed. As the judge that round, I said only, "Don’t get crazy,"but one of my friends still wrote douchecuntbitchslut!
Shit eating pin-head and take a flying fuck at a donut.
Or doughnut, as the case may be.
The one I use when I’m really angry: ass sucking donkey fucker!!!
Two-dollar Thundercunt.
A rolling donut, of course. 
I like using the Farscape word “frell”
Frelling sod off, or frelling puta for that multicultural cusser.
I always liked “syphilitic donkey-raper”.
And one from Family Guy (Stewie, of course): “Damn it to pus-spewing, blood-gutted Hell!”
I like “cock-socket” (because it’s another way of saying, well, you know…)
Also in the running is “cum-bucket” (because it’s just so horrible a description for a human)
And last, but not least “you dirty-bird!” (because people seem to leave me alone after I use that one 
)
I’m a traditionalist… something like “curse the milk on which the priest who baptised the whore that birthed him was fed” is my idea of a basic cuss. Yeah, Spanish lends itself to lots of subordinate clauses, why do you ask?
I once called a very-much-Southerner a Yank. She laughed, after realizing that it did touch a nerve more than if I’d called her something less personal.
“You unrecognized spawn of a murloc and a festering boil” works well for WoW addicts. You can substitute a race from the other faction instead of the boil. Calling a tauren “ugly son of a gnome” works well. Oh, and calling someone an insult usually reserved for the other gender, like “you son of an elf” if they’re female is similar to the Yank thing, people go into 
mode before deciding whether to get :mad: or 
Simple but effective, translated directly from marathi, and more powerful, I think, than its maternal equivalent:
Sisterfucker.
I’m quite fond of (straight from the Internet) “cockmongler”.
And my friend once came up with “minging motherfucking bastard of a bitch”, which never ceases to amuse me.
That’s a great one. The wedding planner guy in Monsoon Wedding uses it about 100 times. That’s the only other time I’ve heard it.
How bout fuckwhistle? Nobody ever says fuckwhistle anymore.
Others along that theme
Assclamp
Fuckerballs
Baglicker
Prick-bastard
and of course; douche-nozzle
I’m still partial to the classic “cum burping gutter whore”. Good old Anglo-Saxon never lets you down.
Goat-felching poltroon! Combines a bit of the new and old, don’t you think?