si 

Abbr. Simple Simon. Individual renowned for extreme stupidity and slowness of mind.

"Jog on you si - you're as thick as pigshit" or "he's a proper si that one, thicker than a King Edward yoghurt"

si by Phileas May 20, 2008

si 

synthetic intelligence.

Artificial intelligence derived from synthetic materialism.

SI is the only path to achieve artificial intelligence.

si by sandraxine June 20, 2018

SI 

self injury.

cutting, carving, bruising, welting, etc.

you: damn... i hate emos.
me: ......
you: you SI?!?
me: ......

SI by 341103001 August 29, 2007

SI 

Sports Illustrated

I done read SI.

SI by Andy L August 3, 2003

Si 

An unbelievably rich cunt (richer than Bill Gates) who wears a monacle and probably has other characteristics but none you really care about.

Also likes boys and sniffing the sweatline under fat guys flabbing man breasts.

Brian has loads of money for beer tonight. He could do a Si and buy the pub free drininks all night.

Si by Bobby Charlton March 18, 2004

SI 

sexual intercourse sex hanky panky hot hottie awesome cool sexy 1. a word and hand-sign created to refer to sexual intercourse in a way unknown to rejects, spazes, and especially older, uncool adults, so your conversations remain esoteric.

2. this term can take the place of words such as hot, hottie, sexy lady, ect.

3. SI can also replace cool, awesome, ect.

ex1: Things are really going well with my gf. I think SI is an inevitability.

ex2: Whoa! Check her out! SI at 10 o'clock.

ex3: "Hey, there having free food at the party, and there's no addmission price this time!"

"Really? Aw, SI man!"

SI by Oddjob 007 September 28, 2006

SI 

Socially Inept.

Seen in episode 13 of "Rugrats: All Grown Up"

"Lil, your brother is what he called SI, you know, socially INEPT"

SI by Johnny Skeets September 18, 2005