Dr Egon Spengler: There’s something very important I forgot to tell you.
Dr Peter Venkman: What?
Dr Egon Spengler: Don’t cross the streams.
Dr Peter Venkman: Why?
Dr Egon Spengler: It would be bad.
Dr Peter Venkman: I’m fuzzy on the whole good/bad thing. What do you mean, “bad”?
Dr Egon Spengler: Try to imagine all life as you know it stopping instantaneously and every molecule in your body exploding at the speed of light.
Dr Ray Stantz: Total protonic reversal.
Dr Peter Venkman: Right. That’s bad. Okay. All right. Important safety tip. Thanks, Egon.
(Ghostbusters, 1984)