"Trip to the vet" joke

Three Labrador Retrievers - 1 brown, 1 yellow and 1 black - were sitting in the waiting room at the vet's when they struck up a conversation.
The black lab turned to the brown and said, "So why are you here?"
The brown lab replied, "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 asked, "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 turned to the yellow lab and asked, "Why are you here?"
The yellow lab said, "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 turned to the black lab and asked, "Why are you at the vet's office?"
"I'm a humper," the black lab said. "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 got out of the shower and was bending down to dry her toes, and I just couldn't help myself."
The yellow and brown labs exchanged a sad glance and said, "So, Prozac for you too, huh?"
The black lab said, "No, I'm here to get my nails clipped!"