It's usually CBT that causes it (or T/D). I always like to know if a sub has a hair trigger so I can avoid it. Frankly I don't care much about a subs orgasm. I want to keep going, but sometimes less experienced subs can't get back in the head space. That's a bummer.

My funniest PE session ever: I was going over "the rules" so we were only minutes into the session - I grabbed the base of his cock, squeezed and and said, "Nothing is allowed to escape from this thing without My permission." He erupted. All I could do was laugh and laugh and laugh. After he cleaned up his mess, we continued and I decided to make a game out of how many times he could erupt in his allotted time. He was a hoot and we ended up having a great time.

The walk of shame is the worst - try to get through it and continue if you can. Most Dommes will understand that you will need a new build up.