Obviously it was a non smoking room and one of your fellow guests was not able to understand or to accept.

So what it the value of the inconvenience of having an ashtray in once room? And what it the value of the inconvenince of "smelling" some old smoke? When checking in just before midnight and checking out probably in the morning I personally would not even think about and not care about starting a thread on FT but would want to sleep.

Plan number 2 would be to complain in the morning and to give them the two ashtrays on checkout and to complain with a grim face like and see how the react.