geek: someone who works too hard, is more intelligent than usual, and is slightly unattractive.
"Bill Gates is kind of a geek."
get it: to understand something.
"Sorry, but I just don't get it."
get naked [possibly offensive]: to completely relax and have a good time.
"Let's get naked tonight!"
"There must be a glitch in this softwware."
go bananas: go slightly mad.
"This project is causing me to go bananas!"
gomer: a dumb person.
"Stop acting like a gomer!"
goof (1): a silly and foolish person.
"What a goof you are!"
goof (2): make a mistake.
I really goofed on the test today."
goof off (1): waste time.
"Stop goofing off and help me clean the house!"
goof-off (2): someone who wastes time and isn't serious.
goof-off never does well in school"
goof up: make a mistake.
"Oh no! I really goofed up!"
"Kids always make me feel goofy!"
"Have you washed your grabbers, Benjamin?"
grand: one thousand dollars.
"He's making over a hundred grand a year!"
"Have you ever smoked grass?"
"Where's the grub?!"
grubby: not clean.
"I always feel grubby in the morning."
grungy: unclean and stinky.
"Grungy people are not allowed in Dave's house!"
gut: a person's stomach; belly.
"Dave is getting a big gut because he loves chocolate ice cream and beer!"
guts (1): courage.
"It took a lot of guts to ask his boss for a raise."
guts (2): the nature of something.
"Let's get to the guts of Dave Sperling!"