Glorified versions of the Aristocrats joke reflect nothing but the filthy mind of the attacker. If you really want to get an insult to work, you've got to hit someone right in their deepest insecurities.
Like walking past the female coworker who constantly frets about her appearance while she's having lunch and say "Might want to go easy on the food there before that man of yours dumps you for someone thinner."
That's not to say that an Aristocrats-worthy insult doesn't have a place. I'm fond of "You're so ugly the only way you're gonna get pregnant is for some guy to blow himself and spit at your crotch." (stole that joke from P.J. O'Rourke, incidentally).
