I think you can regret some of the things you did when you were young and stupid, but I don't think you can regret actually being young and stupid. Some of the most intense, exhilarating, amazing moments will happen when you're young and stupid and don't know any better; and you will never quite be able to bring yourself to repeat those moments because the hangover/heartbreak/depression/bankruptcy that follows them is what jolts you out of being young and stupid. You're only brave enough to do things when you're ignorant of the consequences, and I think everyone needs those moments. Eventually you will stop deathwishing that guy or puking at the smell of that drink, but you will remember the reckless things and destructive people who made you happy.