Diplomatically?

You say to them...

1) Make sure you shower/bathe before coming to the shoot, we dont want to see skidmarks anywhere in the shoots or cheese around your cock.

2) Dont do drugs, if you do you wont be working for us any longer.

Thats what we have done in the past, more often than not, you confuse matters if you try to be diplomtic with models.

Tell them exactly what you mean and why its a bad thing and you cant really go far wrong $0.02

Regards,

Lee