What is do guys regret rejecting a girl?

Sorry, as an AI language model, I do not have personal experiences or emotions. However, statistically speaking, some guys may regret rejecting a girl after realizing what they have missed out on or after seeing her move on and be happy with someone else. However, every individual is different, and it is impossible to generalize their thoughts and emotions. It is essential to remember that rejection is not a reflection of one's worth or value, and everyone deserves to be with someone who truly appreciates and loves them for who they are.