A reply to something not true, or reply to any fact that Dwight Schrute does not agree with.
Jim Halpert: Question. What kind of bear is best?
Dwight: That's a ridiculous question.
Jim: False. Black Bear.
Dwight: That's debatable...
1. Adjective: describes a person who is "false"
2. Verb: the act of "falsing" someone
"Did you see what Rick did to Micheal last night?"
"Yeah, he spat in his drink and then had sex with his girlfriend. He's the falsest chap."
"Can I get a lift with you tonight?"
2."Will you get me a bottle of JD when you're at the off-license"
"No, I've no money!"
"Ahh, you're falsin' me, chap"