The "Stag", "Bachelor" Party is an old established custom, stretching back before ancient roman civilisation 

The Horned God referred to in both Celtic and early English mythology was a symbol of all things male.


The Celts called him Ralph, the God of Stag

                              Hail to Ralph, the God of Stag

In pre-Celtic times, legend has it that males worshipped a large hairy god who sported antlers, ran around with the wild hunt, farted and belched at inappropriate times, never bothered putting the toilet seat back down, stayed out far too late without ever phoning home to warn anyone, willingly drank alcohol to excess and regurgitative quantities, and solicited the favours of ladies who were happily prepared to remove all their clothing for the appropriate fee. 

Stag Party "Performer" Dated 69BC

And to this very day, men pay homage to their ancestors by referring to the grooms last night of freedom as the "stag party" -
a celebration of manhood and beer.

OFFICIAL STAG PARTY DEFINITION: A stag party (also called a bachelor party, stag night, or bucks party) is a party held for a bachelor shortly before he is married, to commemorate his final opportunity to engage in activities a new wife most certainly will not approve of, and to spend time bonding with his male friends. Any decent stag party will most certainly involve activities such as going to a strip club, hiring a female stripper or escort, drinking alcohol and gambling.

DID YOU KNOW?
That in the 1930s, 'stag movies' were x-rated films shown at 'stag parties' for men about to be married?

That going "stag" to a dance meant going without a date?

That standing in the "stag line"  was a line of men waiting for a dance with an unattached woman?