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5.
When a person, not having real friend's make's them up. ie imaginary
Oh, look it's sarah, she has to make insta-Friends cause she's to much of freak to get real one's. Let's go laugh in her face.
by Fitz Bailey January 21, 2007
 
1.
The most annoying people in existence and usually leave you guilt-ridden when you get rid of them. Usually are people who you have no interest in gaining any form of relationship with, but one friendly remark and you have a new buddy.
EXAMPLE 1

Terry: *Sitting on the bus*

Hoit: Hey Terry, nice shoes

Terry: Uh, yeah...thanks...

Hoit: OH MY GOD we are exactly alike

Terry thinks: Goddammit insta-friend...

EXAMPLE 2:

Jack: Hey Josh, do these stick-

Josh: STFU GTFO

Jame: Hey man, wtf that was harsh

Josh: I don't need another insta-friend
by The PBEEF October 01, 2009
 
2.
When you meet gregarious friends of a friend of yours and they automatically become your friends, too. While there's potential for meaningful relationships, instafriends usually remain cheerfully superficial.
"I went to a party with Frank, he introduced me to Sally, Joe, and Bob. We all exchanged numbers, yay, three instafriends!"
by hypello November 23, 2003
 
3.
1. Upon your first encounter with a person formerly unknown the instance where you are BFFL. Instafast like the drive thru at Starbucks.
Upon returning from cruise one Navy Sailor to a Navy Wife instantly hit it of as BFFL over a few beers and a wicked game of Rummy.

BAM Instafriends for life!!!!
by !3blackcats December 17, 2008
 
4.
Becoming friends instantly because of some event.
Lana is not going to become insta friends with her Dad, who was never in her life, just because he gave her a credit card.
by MACbihh April 03, 2009