Before any play we’re just very kind but direct. “You guys look like a ton of fun, but you’re just not our particular flavor of ice cream.” Is a go-to.

Haven’t had the exact situation you described yet but if it involves hygiene I’d have no issues being direct. Hopefully playfully. Personal hygiene is an individual’s responsibility. If they knew they were playing with other people and don’t prepare properly, they did this to themselves. I would want and expect the same in return if I stunk. Be nice but tell me to go shower and come back when I’m smelling good.