My brother came over tonight. He said, "I'll bring some beer." I wasn't really in need of beer or anything, but I figured we'd get some chips, drink some beer, and play some Nintendo. When he got here, he had about six cans of Coors Light. In my family, it is pretty well accepted that Coors Light is not beer.
If you find yourself in a similar situation, here's what you do: ask, "Would you like yours in a glass?" Then, before you receive an answer, your your "beer" into a pint glass. The sight of the sickly yellow liquid will immediately shame your guest who will then say something like, "Is the pizza place down the block still open? We could go get some real beer."
I didn't take him up on it, but it was amusing because he did immediately become quite uncomfortable at having brought Coors. I had some anyway, as it was a tolerable drink to have with some chips, salsa, and monkey ball.