Thread title doesn't explain it properly but I mean those moments looking back, no matter how soon or long ago, you wish you could have said/did/acted differently looking back in hindsight.
My most regretful one was when I was aged 8 in 1994 and I had gone to my friends house and his dad said "I've got no problem with your lot, it's the paki's I can't stand" and ugh, I remember feeling pleased he had no problem with my skin colour but looking back what an ignorant and horrible statement to make especially to a child and looking back, as an adult, wish I could have said something back to him.
Another one was when an old boss told me I was useless and pointless. Wish I'd told him exactly how useless and pointless that he was in running a business when all the staff hated him but I was 15 and didn't have the confidence and just accepted it meekly.
Yours?