After two years of mystery regarding the origin of my recurring hip bruise, the source has been discovered! When I'm stopped at lights I lean my bike in a way that the front tip of my saddle leans on my hip.
So for the last two years I've had this bruise that comes and goes and I look at it and wonder, "What the hell? Do I sleepwalk? What is that from??" This morning while waiting at the light my seat hit my hip and it hurt, right on the bruise. Doh!