The student comes up to the professor, "What is this, why did you grade me an 80?"
The professor looks at the exam again, "Yep, an 80 is what you deserve"
The student takes the exam back, and asks "If I'll bite my own eye, will you give me an 85?" The professor is surprised, but still he agrees, at which point the student then takes out his glass eye - and bites it.
The shocked professor then takes the exam back, and marks it 85. The student then says "If I'll bite my nose, will you give me a 90?" The professor is once again shocked, "He can't pull out his nose" he thinks to himself. He finally agrees, at which point the student takes out his dentures, and bites his own nose.
The professor then once again takes the exam, and marks the grade 90.
The student then makes another offer: "If I'll get up on this table, and pee the perfume Coco Chanel on you, will you give me a 100?"
The professor now has to see what this kid can do, so he agrees. The student goes on the table, and pees all over the professor, the professor's shirt is soaking wet, as he goes to to sniff it. "What the hell?! This isn't Coco Chanel! This is piss!"
The student then goes "Fine, we'll leave it at 90".