Just 'cause you don't have a switch, don't get angry at me, baby

- fra et Rolling Stone-interview, 1991:

Asked if he and Marsha plan to have another child soon — Zachary is the product of his first marriage — Father Man nods and begins talking animatedly to a part of his body that he usually refers to as either Mr. Happy or Lumpy. "We have a few left, yes?" he says. "Those ninja sperms! Those ones that blow a hole in the diaphragm! Those ones that get through, no matter what!"
For the next few minutes, Williams is "on." Occasionally, when the actor lapses into his celebrated shtick, the routine seems forced and perfunctory. He seems to be clowning around simply because he knows he's famous for clowning around. Other times — like now — his short-circuited patter is literally breathtaking. Williams is not tap dancing on a hot plate; he's just having fun.
Eventually, Williams skids to a stop, looking wild-eyed and a little winded. "Fuck, it's great to play," he says. "Who wants to be deeply serious all the time? That would suck, I think. But I'm just now getting to the point where you realize, 'Wait, you don't have to play all the time.' It's exhausting, and you have to save something for when you come home. Marsha gets asked that all the time: 'He must be really wild at home!' The truth is that if I were, she wouldn't be alive. That type of freneticism is insane."
Hence the Robin Williams who walks into a room like everybody else does. Who talks for hours without once doing his mad-scientist laugh or standing on his head. It's true that Williams still can't go ten minutes without telling a joke about how hairy he is — these jokes always involve either Darwin or the film Quest for Fire — but for the most part he's "on" when he feels like being "on," and he's "off" when he feels like being "off."
"I used to hate that," Williams says. "People would say, 'You're on now. Do you always have to be on?' " He gets another glint in his eye, and — in a voice that's part Robin Williams and part Groucho Marx — he turns to address an imaginary accuser: "Yeah, sometimes I do. Around pricks like you — around raving assholes like you — I really like being on. It makes it easier. 'Cause being off would be pretty fucking boring."
Here, revving his engines again, Williams drops the Groucho inflection and picks up a little street sass. "Just 'cause you don't have a switch, don't get angry at me, baby," he says. "Just 'cause you don't have the batteries, don't call up and tell me to turn out my light."

Read more: http://www.rollingstone.com/movies/features/robin-williams-fears-of-a-clown-20140811#ixzz3AB7xK9A7