2. Saying something like "Don't contact me if you're fat."

Guys who write this in their profile — and yes, they're usually dudes — always say as a caveat that they're "just being honest." But in online dating, honesty isn't the best policy; it's dumb. You don't need to spell everything out, especially if it's something obvious like how you want to date someone you're attracted to. That's called tact, buddy.