I personally feel that sploofs are overrated. They do greatly reduce the scent, but a nonsmoker can still tell fairly often.

Smoking in a bathroom/bedroom is always shady (unless it's your own house, but it doesn't sound like it).

Go outside, or if you really can't get out, garages work way better than a bathroom. They're bigger, have a smell anyways, and typically have some sort of ventilation that leads outside. Smoking in a garage with a sploof, exhaling towards something that vents outside, with some febreeze or whatever after, will probably cover you. But smoking inside is always risky if you're trying to hide it from someone.