The nerd moment in question is usually down to interpretation, but it usually adheres to stereotypes of the word, Nerd.
"I spent half the day tweaking and modding my PC systems so it operates more efficiently" *Nerdgasm*
Guuitar Nerd 1 "Dude, did you see that 7 string sweep picking with the string skipping"??
Guitar Nerd 2 "Yeah I did, had a nerdgasm it was so damn good"
Nerd 2: " Well I don't know, let's have a Star Wars slumber party with Bob and Frances and make a list of reasons!!"
Cool Bystander: "Ooooh I just had a nerdgasm!!"