A moment that has happened sometime in the past (usually the night before) and is tremendously embarrassing to even think about never mind speak about. When a 'No' moment has been recalled usually the victim will come out with a frustrated
"NOOOOOO!" groan or even a delicate "no..." mumble. 'No' moments are usually caused by alcohol and cringe-worthy social situations.
"Aww man you were totally wasted last night and you tried to pull Jessy! But she refused your sexual advances! Gutted for you!"
"Awww... NOOOOOOOOO!! ARGH"
"Was that a 'no' moment?"
"Aye, it was"