The high point of sexual excitement, and/or climax while thinking about, listening to, watching, or being in the presence of Adam's ultra-uber-out-of-this-world sexiness.
To get herself in the mood, Peggy Sue simply went through each role Adam swings in her mind and was on her way to an Adamgasm in no time.
Otter 1: Did you see that video of Adam impersonating us?
Otter 2: YES! It was so fucking hot I had an immediate Adamgasm!
Casting Director (whispering to her colleagues): You'll have to excuse me for a moment, if I stay in this room any longer listening to Adam's sultry vibrato I'm going to have a Adamgas---....shit...shit...IT'S HAPPENINGGGGGG!