The obvious answer, to me, should be not only refuse, but remind everyone who is on duty that they're on duty. I'm not the kind of person who cries to the captain or station officer if someone called me names, but if there was any drinking going on and I couldn't stop it before it happened, the officer would be my next step. Really no different than if I seen an unsafe condition on the apparatus floor, like a wet floor, tripping hazard or damaged equipment. I'd try to correct it myself and if I could not, report it up the chain of command to be dealt with.
The reason questions like this are stupid is because this scenario shouldn't even be possible in the first place. In this day and age it should be widely accepted that drinking, no matter where it happens, and going on calls is absolutely unacceptable.
"No one ever called the fire department for doing something smart"
"If you don't like what you see, Why don't you fight it?
If you know there's something wrong, Why don't you right it?"