On the sly 

To do something on the sly is doing something sneakily, like a ninja.

"Check it out, I stole this on the sly."
"I'm skiving off school, on the sly of course."

On the sly by Naevai April 3, 2009

on the sly 

To be on the sly, the active of sly. You can do something on the sly, maybe stealing something funny and legendary, like mine and Jimbo's road bollard. You could also have 'slying it'

"We took that bollard on the sly"
"Tonight we're slying it/on the sly"
"Come on lads, here we go, on the sly on the sly"

on the sly by Ybot December 28, 2005

macking on the sly 

Covert flirting between two people. Because they have to keep their true feelings for each other secret, for whatever reason (i.e. they work together, one is married, etc.).

"Those two can't seem to stand each other! They're always fighting over something!"

"Wrong, man. It's all a front they put up. They're actually macking on the sly."

macking on the sly by D. Gould March 8, 2006

Susan on the Sly 

A secondary girlfriend, one that is around constantly and annoys you and your personal friends.

Heather - Hey can I have your boyfriends friends phone number?

Girlfriend - No, he says you are a Susan on the Sly

Susan on the Sly by JT Stranganopolis March 31, 2009

sex on the sly

Cheating or trying to cheat when you have a spouse or significant other. Those looking for sex on the sly are liars and cheaters.

Nancy: Did you hear? Monty's lookin' for some sex on the sly. Jack saw him hit on a girl at the club.

Alice: You mean Monty, Sally's husband?!

Nancy: Yeah, can you believe it? He seemed so sweet and caring to her. Go figure.

Alice: Uh huh, another cheater.

sex on the sly by mad megawoman August 6, 2011