I like when guests play my games; that's part of the joy of having them.
The only rules are: no food or drink near the machines (I make exceptions for close friends with beer, just not actually on the game; I should really get some of those beer caddies) and no actual abuse: really rough nudging or shaking or hitting/kicking the games.
If kids or adults chimp-flip, I try to educate them on good play techniques.
RussM