When you are f***ing your girlfriend and then she tells you that you f**k like your guys' dad.
Then you f**k your mom and she says the same thing.
Listen up, smarty pants, Explain Bear is here to drop some knowledge on your thick skull. This joke is all about incest, which is when you get down and dirty with a family member. In this case, the dude is boinking his girlfriend and mom, and they both say he's got the same moves as his dad. I know you are too dumb to know this, but most people don't go around sleeping with their relatives. It's a big no-no, and it can mess you up, which is probably why you find this funny, you low IQ idiot.