What? What? Who can't take a joke

I have a few friends that I consider family.  Anytime they drive thru town they stay at my house.  They shit, shower, shave, eat, and sleep under my roof with nothing expected in return.  They drive my car, they go out to eat with my wife when I’m not around, and occasionally I’m forced to clean up after them a little.  This has been going on for years and there has never been a single problem.  Yet, if one of them stood in my living room and screamed at me for 20 minutes for no reason, I’d punch him in the fucking mouth.  If they walked thru my basement and threw everything they touched on the floor and laughed about it, I’d set their car on fire.  Complaining about the food on our table would result in me dumping the plate in question in the trash, then sitting down to finish my meal without comment.  Yelling at my wife in any setting would warrant an ass stomping of epic proportions.  The fact is the end result of any of this behavior would be me bringing the relationship to a halt.  I wouldn’t allow this person in my house, there would be no kind words exchanged, and when I drove past them I would probably swerve in their direction.  

So if would respond so severely to this behavior from someone I’ve known for 10-20 years, why do I have to forgive a kid who’s only been living here for 6?  Did the kid help me hook up with my wife?  Did the kid bail me out of jail?  Did she help me move?  Let me borrow her car?  “Loan” me some drugs when I was using?  Nope, on the friend scale both my kids are free loaders.  They are Paul Hooper circa 2005.  In summary I think when they turn 18, they are both going to watch a “best of” video followed by a swift boot to the head.  I hope in 13 years I can still sweep the leg.