Every Friday night, I pregret that I will go to the club. I know I willstand there like an idiot and won't talk enough game to bring anyone home with me.
Seeing yourself in the future, and feeling regret for doing/not doing something in the time between now and then.
"I became my 60-year-old self and was overcome with regret for wasting so much time on the internet, that when I snapped back to "now", I felt immense pregret, for the time yet to be wasted."
The the feeling you experience when you're about to do something you know are going to regret but you do it anyways.
This includes but is not limited to: performing a dangerous or painful stunt in order to entertain your friends, being put in an awkward situation, having sex with an ugly girl, eating something you know is going to taste horrible, paying to see a bad movie or doing powerful hallucinogens for the first time.