The best prank I've ever pulled...
What was the prank?
I've sent many girls fake dick pics.
Sending dick pics is hardly a prank and more like sexual harassment. You should apologize and never do it again.
It's so funny, I don't care about them anyway.
What may seem funny to you can be upsetting to someone else. Sending an unsolicited naked picture, fake or not, is wrong. There are other pranks you can play that don't harm anyone.