It's on my right arm, about two inches above the elbow, on the medial edge, the side that would normally rest against my ribcage.
When I feel it with my left hand, my right arm tells me it's a bruise, but my left hand tells me it's a free-floating fatty lump. It hurts.
If it's still there in another few days, I'll go and get some doctor to feel it.
Oh, and in other news (and thanks to elfs for the link), the people of America are under attack from comic books now. Be vigilant.