Ick no workout clothes in public...not even if you're going clubbing. Like mentioned before, a nicely fitted cotton t-shirt is ok, especially if it's vintage or vintage-looking. Polo shirts or not-too-baggy button downs are hot too. But if you're going the t-shirt route, don' go too tight--there is a guy in one of my grad classes with an amazing body, but his shirts are always so tight that you can see his pecs move up and down while he writes, talks, and with basically every other little movement he makes...it's so funny.