How do you know when a bassplayer is at your front door?
You dont. He just stands there mumbling to himself "whats the point of knocking? No one is gonna pay any attention to me when i go in anyway. May as well just go home now..."
How many roadies does it take to change a lightbulb?
None. Roadies dont change lightbulbs. He'll take it apart, repair it with gaffer tape, change the screw mount to bayonet mount, finds an appropriate patch cable, and re-install the bulb fifty feet from where it should be, so that the guitarist likes it. But he wont change it.