The Naughty Bride Says:

Q. When the groom has cold feet, how much "dutch courage" should a best man serve?
A. Responsible people never go through with things they need to be drunk to do, but since you're just trying to relax, priests recommend an absolute maximum of two shots of alcohol from a hip flask, even for frat boys. If the only thing available is communion wine, administer no more than two glasses.