Haha! I didn't know the shit it my pants one. I'll have to try it out. The phrase, I mean.
I like "bei mbak", which means - best I can tell - idiotic. But it sounds a lot like "bei bai", i.e. "not bad" or Mandarin's "bang" (awesome). So, of course, I feign flattered when my wife uses it on me. "But you're very bei mbak, too, Dear."
Mai gong wa e pai wei - Lit: Don't speak my bad words. Don't talk smack about me.
Kua sa xiao - What the hell you looking at? I've been warned this can be explosive.
Li mai ga wa po lan pa - Don't pat my testicles. Or something like that, meaning don't try to use flattery with me, or don't be patronizing. Very crude, obviously, and can get a good laugh or negative reaction, depending on the audience.
You might notice I'm not using proper romanization here. I like this website's http://weber.ucsd.edu/~dkjordan/resources/PronouncingTaiwanese.html
guide to pronunciation and spelling, though I haven't taken the time to really learn it.