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1.
When you put your dick in your sister.
I'm so horny if I don't insis soon I think I'm going to explode.
by Sofa King We Todd Did March 14, 2007
 
2.
Term to describe when someone tries really hard but just cant get the job done.
Named after the semi-famous german Unreal Tournament player inSi.

It originates from the german Expression:
"inSi kann nix!!!" (which roughly means "inSi sucks!!!")

The 3 exclamation marks have to be used to put more emphasis on the message.
"Wow, koby failed to sink that Buzzer-Shot and the Lakers lost? He pulled a real inSi off right there."

"Honey, I know you tried your best and the potatos taste good,
but i think the meat is a bit of an inSi."
by dermeisterrr November 17, 2008