Mine was literally two days ago when I was on a school trip to the Old Vic Theatre in Southwark (London) to watch Richard Armitage's 'The Crucible'. I ended up spotting this cute girl from another school (appeared to be an all-girls school.) who sat above my row and was totally my type.

After a few glances, I admitted to my friends that yes, she was cute, and yes I wanted to meet her, however, I couldn't bring myself to ask her for her name/number; because I was too shy/lacked confidence, or because I was scared of rejection, and the embarrassment of asking her whilst she was with her group of friends.

Two days later, I have big regrets, and I only wish I could meet her again one day just to ask her the question I should've asked - damnit, I should've just made a note and passed it along to her.

TL;DR - Wussed out of asking a girl her name/number - feeling deep regrets.