I've read that the head of men's penises are very sensitive, or the vein on the underside. But my boyfriend doesn't seem to be affected by it too much. In fact if it wasn't for the fact that he thrusts into my mouth when I go down on him, I would think he was completely unaffected. Could it be my technique or is he just really unresponsive or maybe even a little hardened by sex after indulging (with the same girl) in the past?