ISF 

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!

ISF by sindrix December 11, 2009

ISF 

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.

ISF by JNL January 11, 2005

ISF 

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.

ISF by Jocelynnn October 19, 2005

ISF 

Its So Funny

isf that ur a MOFCAKE

ISF by THE MASTER OF CAKE October 20, 2003

ISF 

Its So Funny

isf that ur gay

ISF by Anonymous September 28, 2003

ISF 

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!"

ISF by youmadbra December 11, 2009

ISF 

Insomniac Shitposting Freethinker, a community of "immature atheists" and "wannabe freethinker" to start a religious flame war

ISF is a place for you to make a racist joke towards religious people

ISF by Sir. B December 1, 2021