I don't mind shamelessly reposting this, I must use some of these in my appraisals:
"Since my last report, this employee has reached rock bottom and has started to dig."
"His men would follow him anywhere, but only out of morbid curiosity"
"I would not allow this employee to breed"
"This employee is really not so much of a has-been, but more of a definite won't be"
"Works well when under constant supervision and cornered like a rat in a trap"
"When she opens her mouth, it seems that it is only to change feet"
"He would be out of his depth in a parking lot puddle"
"This young lady has delusions of adequacy"
"He sets low personal standards and then consistently fails to achieve them"
"This employee is depriving a village somewhere of an idiot"
"This employee should go far, and the sooner the better"
"Got a full 6-pack, but lacks the plastic thing to hold it all together"
"A gross ignoramus - 144 times worse than an ordinary ignoramus"
"He certainly takes a long time to make his pointless"
"He doesn't have ulcers, but he's a carrier"
"I would like to go hunting with him sometime"
"He's been working with glue too much"
"He would argue with a signpost"
"He has knack for making strangers immediately"
"He brings a lot of joy whenever he leaves the room"
"When his IQ reaches 50, he should sell"
"If you see 2 people talking and one looks bored, he's the other one"
"A photographic memory but with the cap over the lens"
"A prime candidate for natural deselection"
"Donated his brain to science before he was done using it"
"Gates are down, the lights are flashing, but the train isn't coming"
"Has 2 brains, one is lost, the other is out looking for it"
"If he were any more stupid, he'd have to be watered twice a week"
"If you give him a penny for his thoughts, you'd get change"
"If you stand close enough to him, you can hear the ocean"
"It's hard to believe that he beat out 1,000 other sperm"
"One neuron short of a synapse"
"Some drink from the fountain of knowledge, he only gargled"
"Takes him 12 hours to watch 60 Minutes"
"The wheel is turning, but the hamster is dead"