Insufficient Funds (lack of money)
Bobby Chong is looking to buy 2 doughnuts for 50 cents each. The cashier lady says that will be; a dollar seven total. Bobby Chong whips out the B.C(Bank Card), swipes, punches in the pin and waits for the thumbs up for approval then 3 letters in Capitals show up on the machine; ISF. Cashier shakes her head in shame and pitty. Bobby curses and walks away for the counter doughnutless; and realizes that he will never step foot in another Tim Hortons again due to ISF...$1.07 damn. How embarrassing.
by JNL January 11, 2005
Top Definition
ISF is Instant Skullf***, one of the best competitive Left4Dead teams in PC Gaming. They've performed in Newegg tournaments, Alienware, and gXl. Ranked in the top ten of Left4Dead teams in competition.
ISF just pwned our faces!
by sindrix December 11, 2009
I'm so fucking sorry.
Yo...I fucked your girl...ISFS
by Spawn 'o January 11, 2015
I'm So Faded
You know what IS-F from Lexus stands for? "I'm So Faded" Brah!!!!!!
by lcr49 July 22, 2009
icky sexual feeling; the kind of feeling you get when something makes you uncomfortable to think about or see, i.e. incest, your English teacher naked, etc.
That creepy guy who works with me looked me up and down and said, "Nice shirt." and I got total ISF.
by Jocelynnn September 23, 2005
Its So Funny

isf that ur a MOFCAKE
by THE MASTER OF CAKE October 20, 2003
ISF means "instant skullfuck". To isf someone is to pwn or destroy someone completely, such as in day to day life, sports, or in video games.
"We are going to ISF that that team later in dodgeball!"

"My girlfriend ISFed me earlier when she dumped me!"
by youmadbra December 11, 2009
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