Maybe a store clerk referring to you as "guy" or "buddy" (those are bad examples because there's a good chance they're pretty innocent, though sometimes you can tell there's a subtext of condescension or an attempt to belittle).

Does a cool guy just let it bounce off of him like water off a duck's back? When I ignore something like that, I can't help but feel a little sore about it, though it usually fades after 10 seconds.