We had a strange policy at one point in the last club I worked at. It was a combination of BYOB and full-service bar; usually they're one or the other, and were actually against the law, but this bar and 3 others in the state somehow grandfathered themselves in under a previous law.
It was free admission if you were buying your booze there, but $15 if you brought your own. Of course, this created a few problems, and you'd be amazed at the lengths some people went to smuggle in booze and not pay a cover.
The best one I ever encountered was during my last week there before the flood wiped out the business. This guy comes in, says he's a vet, shows me his service card and his prosthetic arm. Normally it's $10 cover for vets, and he was carrying a 6-pack, so I told him no charge and thanks.
Several hours later, making the rounds, I saw the six pack sitting unopened on his table. When he saw me he hurriedly pulled a small clear plastic tube out of his mouth. I went up, stared at him for a few seconds then asked him "Show me that thing".
He laughed and showed me a custom flask system hooked up to his prosthetic arm, with a tube leading from the flask of whiskey up his arm to his shirt collar. When he wanted a drink, he'd look around, pull the tube up and take a swig.
What was I gonna' do? I shook his prosthetic hand, laughed and walked away.