Oi

Oi, or Oy is cockney now mebbe, but its Yiddish roots go way back. In Yiddish it's a general expression of existential angst. Its roots are pure Hebrew, where "Oy" means "woe".

"Oy, so you think you have troubles?"

wifty

Adjective, origin unknown. Flaky, space-cadet, but in a *nice* way. Not generally used outside the Philadelphia PA region.

That wifty chick went out on her lunch hour and bought roses, but forgot to cash her paycheck!

maven

"Maven" comes to us from the Hebrew, by way of Yiddish. In Hebrew, "mavin" means "he knows". So a "maven" is someone in the know, a real expert, or maybe sometimes just a self-styled expert.

"You need to decide on a new computer? Talk to my cousin, he just graduated from CalTech, he's a real maven."
OR
"Okay, so you read one magazine article, what does that make you, a maven?"