This is based on situation when person forgets to close his zip. or unzip his chain and shame he has to face.
this joke is full of comedy humor and situation fun
lady sitting alone at a bar sees a man leave the bathroom with his zip
down...she silently tells him, "dude, ur garage door is open" while pulling his zip up he asks with a grin on his face, "did u see my hummer in there?" "nah", she replys, "i just saw a mini cooper with two flat tires"