Guy#1: Hey I'll be right back, gonna hit the men's room. Guy#2: Oooh, good idea, I'll come along with you. Guy#1: Umm, I don't need help, thanks.
Guy#2: Oooh, good idea, I'll come along with you.
Guy#1: Umm, I don't need help, thanks.
Even when unplanned simultaneous access occurs, guys always follow the alternate-urinal rule.
:)