Don't carry a backpack?

Apply some deodorant. Sweat stains that spread to your stripes are unsightly.

Avoid very tight fitting pants. I heard a story once when the guy bent down when he heard a rip (no, not the gassy kind). He also had on white shorts so it was very evident his black pants had torn open. So maybe you should wear shorts the same color as your pants?

I'm sure airlines won't allow this, but I can't stand guys who wear their shirts open enough to expose their hirsute-ness and that biggest faux pas of all - the thick gold chain necklace. God almighty, that is gross.