STRIPES! Especially bold colors or chevron patterns. Everyone thinks horizontal stripes are not flattering, but with careful consideration, I think they can actually be pretty attractive. In fact, one of my favorite shirts is black and grey stripe. Too bad every time I wear it, I get called Pablo.
To be fair, I guess I am the one that hung that poster on the wall. Right on, Pablo. In case you're curious, his were Breton Shirts.