I had an experience once in the back of a girl's truck. I was eating her pussy and my cock was hard, of course. But I was eating for so long, my cock kept getting soft and hard again, and then soft and hard again. By the time I was done eating and fingering her pussy, she wanted to suck me off. I had built up so much cum and was throbbing with anticipation, by the time I got it to her mouth I was semi-hard and exploded as soon as my cock touched her lips. I was surprised as was she. Not as explosive but still felt good.