SU 

S.U. (said 'S-U' not 'sue') stands for socially unacceptable. It can be used in many ways but is often used as an exclamation. It describes situations which are akward, tense, or actions which are inappropriate in a given situation, or simply unacceptable according to social norms.

Did you just ask that complete stranger if you have something in your teeth? SU.

That girl is so werid. All I have for here are two words... SU.

SU by K,K&S April 13, 2007

su 

Shutup, a cleaner version of STFU (Shut the fuck up)

<Hex> I had such a dirty shit just now!
<Terran-Ghost> SU, for the love of god SU!

su by Terran-Ghost June 3, 2003

Su 

Usually seen in Snapchat Su in slang means Swipe up and or Shut up
It's seen in. Texting not speech

Example "Su who is this "
meaning, swipe up who is this?

Or
Person 1: did u see Madison's Story??!
Person 2: no, show me
Person 1 k, I'll send u a screen shot
Person 2: SU! SHE GOT A NOSE PIERCING??!

meaning

Shut up! she got a nose piercing?!
Shut up in the way of saying, No way or Omg really?!

Su by Wizz32 October 6, 2019

Su 

Straight up.

I fuckin’ hate people who speak without thinking, su

Su by GuyOnTheInternet69 February 20, 2019

su 

A peticular person close to you that you use as a nickname when they are to be honest, doing really anything.

"Pelon, you make my life."
"SU, YOU ARE SO CUTE!"

"why are you not answering my phone calls?"
"don't worry about it, su! :)"

su by sincerely_su June 24, 2009

SU 

Student Union

You of to the SU tonight?

SU by Someone121111111 January 21, 2011

SU 

Stumbleupon, the social channel surfing network.

I've rated 1000 pages on SU

SU by nome June 5, 2007