Never take your bulletproof vest off in the middle of a firefight
Yeesh, how often does this happen in films? 'Help me get this off, I can't breathe!' Kevlar vests don't work that way. Being shot while wearing one will hurt like hell, and may bruise you/crack ribs even, but taking the vest off isn't going to help, and it's generally unadvisable to do so *when the bad guys are still shooting at you*.