F4 (a poor image, but meh.)
An F4 tornado in Omaha, Nebraska on May 6, 1975.
An F4 tornado that looks like a penis.
F4 also stands for "Freakin' Friday Film Fest" an event that originated when the members when in high school. Each Friday, one member hosts two movies for the viewing pleasure of the other members. Board games, food especially frito pie, and humorous commentary are also welcome additions to the event.
The group known as F4 Inc. was originally formed in Decatur, IL. but also boasts an international member in Germany.
"Oh, I'm having the F4 guys over to watch Killer Klowns From Outer Space and Dr. Strangelove."