This is what I was told by the very kind (and lovely - although I'm gay) FA who ripped me out of the J lav on a LAX-YYZ flight when the guy in the BACK lit up. She, in fact, used the ashtray in that lav to put it out for him.

Apparently it takes a second to nail down WHICH lav the alarm went off in. Tee hee. Luckily with all the tugging on the door before it gave way I had time to zip up. She was mortified, and I told her to relax - she was just doing her job. A few Vodka Tonics and all was well.

And for the uncertain, let me assure you: Authorities met the aircraft at the gate on arrival, and the gentleman in question was lead away in cuffs.