when you're jacking off and you're not really feeling it yet but you cum anyways and you end up feeling horny again soon thereafter. usually happens when you're in a rush or about to get caught.
i was wacking it to some hot pics of jenna juggs 'til i heard someone knocking and i half-gasmed. total buzzkill.
When masturbating, holding back for too long and then letting go, only to find that you've missed the orgasm, but still ejaculated. Disappointing, all the work but none of the reward.
I jerked for 30 minutes only to be rewarded with a half-gasm.