How can you tell if a heterosexual man has been using the computer?
There is sperm on the computer screen.
Computer Usage by Heterosexual Man: A Crude Observation
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Explain Bear
Alright, you knucklehead, listen up! You obviously don't know much about human biology or the internet. The joke implies that a straight dude jizzed on his computer screen. The humor comes from the shock factor and the gross image it paints. It's playing into a nasty stereotype, which makes it extra cringe.