Your mum. Never gets old, and can be used in a variety of situations

Is that your face or did your neck throw up? Lol

I just remembered a good one I got off of Cracked. I think it was by Seanbaby and he was talking about someone who wrote a horrible self-help book or something. "Every time you flush a toilet, four species of fish go extinct." 

"Your face is bigger than a turd".
"Your eyes look very blue, that it is so cold".

"Let me turn around so we can speak equally: Ass to ass."

"Wear a diaper over your head cause shit is spilling out your mouth." Brian from Family guy once.

And really anything with the suffix -ass is almost guaranteed to be good. Examples:

Dumbass
Shitass
Jackass
bastard ass
Shove a foot up you ass!! -I love this one the most- Anyone who watched the show will know this :3

Your face... your ass... what's the difference? (Duke Nukem)

Get off of my internet you demented butt pirate (Random made with some insult generator)

Oh, and my dad uses this a lot:
(I'm) not as stupid as you look. (Somewhat a direct translation from my native language)

I thought this one up yrs and yrs ago ((Your So Ugly Even Death Died Of Shock)) i know horrible lol