Allegedly it is the man's last night of "freedom" (until she leaves him and cleans out all his worldly assets) so his pals feel obligated to give him one night of debauchery in hopes he will come to his senses before the wedding.
If the groom goes through all of that and still wants to get married, the bride knows he's been pre-whipped and is sufficiently ready for matrimony.
uh-huh....nice try....as if the bride doesn't have trials of her own to look forward to.
A creative response though :)