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2.
it stands for SPECIAL SEX INTREST.it means your intrested in a certain type of sex, but it's not a fetish.
my recently married friend gave me some sex videos that all had foot fetish porno.later on i thought i developed a foot fetish.but that same friend just told me it was a S.S.I.
by RabidPyro July 06, 2009
 
1.
Student Sexuality Information Service: a student-run, non-profit organization devoted to promoting sexual health on the Brandeis University campus through various services. Services are completely confidential. SSIS maintains a library, holds office hours, sells safer sex products for cheap, acts as a referral service, and does outreach on campus through events. Members of the group are trained peer-counselors volunteering their time.
Students in Shapiro Campus Center.
"Yo, where's your girl goin'?"
"She's goin' upstairs to SSIS"
"Why?"
"Cause I be gettin' some tonight, dawg."
by Sexified February 05, 2007
 
3.
SSI
Screw Some Idiot

If a person haven't had sex for a long time, and he/she's getting more and more annoying (because of this), he/she needs to get laid asap.
"- I can't take this no more, it's been ages I haven't slept with anybody, this is killing me! I'm a nice person, why can't I get someone who would have sex with me? Blah blah blah...
- Girl, you should just ssi..."
by awesomenessHU November 16, 2009
 
4.
SSI
plural: SSI's. Noun. One who works at posh summer internsip and is sexy. Acronym: Sexy Summer Intern.
SSI: Boss, you should take me to dinner/Alaska/drinks because I'm sexy.
Boss: Ok, I'll get you on the next flight.
by The Original SSI's August 02, 2007