I love nerd humour.

[The number] four can be used as an obscenity in some technologically adept circles, replacing the common word for fornication. This usage derives from the fact that when counting in binary on ones fingers, 4, whose binary representation is 00100 is represented by raising the middle finger of one hand, yielding a vulgar gesture. A stronger variation uses the number 132, whose binary representation 0010000100 replicates this gesture on both hands.(Wikipedia)