Slang: to express a thing or person that is purposely cruel, mean and unnecessary, usually when you would not expect it/them to be.
1. Adjective: describes a person who is "false"
2. Verb: the act of "falsing" someone
1. "He was meant to give Tommy a place to stay last night, but he went home without him. He's so false."
"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"
1. Usually describes a hairstyle with a very high fringe.
2.Can also be used to refer to someone with an Ace hairstyle
Originated from the Jim Carrey film Ace Ventura: Pet Detective
"Jesus, look at the size of the ace on yer man."
"Hello Timmy, your ginger Ace is looking quite well today."
"Well, Ace! What's the craic?"