"Three dogs at the vet''s" joke

Three Labrador retrievers - a brown, yellow, and black - are sitting in the waiting room at the vet's office when they strike up a conversation. The black lab turns to the brown and says, "So why are you here?"
The brown lab replies, "I'm a pisser. I piss on everything - the sofa, the drapes, the cat, the kids. But the final straw was last night, when I pissed in the middle of my owner's bed."
The black lab says, "So what is the vet going to do?"
"Gonna give me Prozac," came the reply from the brown lab. "All the vets are prescribing it. It works for everything."
The black lab then turns to the yellow lab and asks, "Why are you here?"
The yellow lab says, "I'm a digger. I dig under fences, dig up flowers and trees, I dig just for the hell of it. When I'm inside, I dig up the carpets. But I went over the line last night when I dug a great big hole in my owner's couch."
"So what are they going to do to you?", the black lab inquired.
"Looks like Prozac for me too," the dejected yellow lab said. The yellow lab then turns to the black lab and asks what he's at the vet's office for.
"I'm a humper," the black lab says. "I'll hump anything. I'll hump the cat, a pillow, the table, fire hydrants, whatever. I want to hump everything I see. Yesterday, my owner had just gotten out of the shower and was bending down to dry her toes, and I just couldn't help myself, I hopped on her back and started humping away."
The yellow and brown labs exchange a sad glance and say, "So, Prozac for you too, huh?"
The black lab says, "No, I'm here to get my nails clipped."