Best
Rosie (Hippowdon) - after that annoying talk show host and fat hippo Rosie O'Donnell
Terrorist (Graveler) - it knows both Selfdestruct and Explosion.
AfroBull (Bouffalant)
Vultron (Fearow) - it comes from vulture and Voltron.
Squidward (male Octillery)
Octomom (female Octillery)
Lucifer (Liepard)
Zamboni (Magnezone)
Foxxy Love (Ninetales) - Foxxy Love is a character on the cartoon Drawn Together. She is a ghetto black woman with a fox tail.
Fatso (Snorlax)
Xenu (Beheeyem)
Satan (Mewtwo)
Worst
Mongo (Tympole) - I got it from the movie Precious, where Precious' disabled daughter was named Mongo. "It's short for mongoloid." was the response Precious gave about her kid's name. I once saw on an old video from around the time BW came out saying that Tympole looked like "an abused autistic child". I'm autistic and even I found that funny.
Balls (Emolga)
Shaniqua (Jynx)
Ape Escape (Primeape)
Orca Food (Pelipper) - It's a reference to this video where a killer whale at SeaWorld was filmed eating a pelican during a show.
Negro (Banette) - This was in Pokemon Pearl, before racist names were banned. Another gem of mine. I changed it because I felt that it was a little too racist. And to make things worse, its ability was Frisk and I think it also knew Trick.
Yenta (Watchog) - In case you don't know, "yenta" is Yiddish slang for an annoying, gossipy woman.
Dux (Farfetch'd) - I used to hate the one-of-a-kind Pokemon in trades since you couldn't choose good nicknames. I mean, you could get a Lickitung, which has lots of name potential, and you got stuck with the crappy name Mark. At least this was rectified in later generations with the introduction of breeding.
Skitit (Skitty), Mimien (Mr. Mime), Tangeny (Tangela) - The nicknames in Generation III were the most retarded. They were all derived from the Pokemon's name. I mean, the Jynx in FRLG got called Zynx. At least the Generation I name wasn't awful. The only one I liked was Ch'ding for Farfetch'd. In fact, that is what I named my Farfetch'd in Black.
Sewage (Roserade) - The fact that it was a male Roserade gave me trouble with nicknames, so I looked for something.
Speedo (Machoke)
RAT (Minccino)
Sexy (Lopunny) - I changed it.
And when I was a kid, I used to name them after fruit.