Based on Happy Days character.... though evolving over the years...
Used for both Male or Female
Defined: Someone who thinks they are a bit too cool... Generally the person who dresses a bit over the top and/or always trying to "one-up" someone else’s comments, whilst tending to overdo everything they try to do....
“Look at that guy over there....what a chachi....!”
Anything trashy, tacky or tastless
Me: "Wow I think that kid wears more makeup than a 14 year old hooker. Or is that a 14 year old hooker?....hmm... nope it's a Chachi"
Nik: " Hey you wanna head to that new bar in town."
Christina: " Hell NO!! That place is totally Chachi"