A colorful method of telling someone to either; a) shut the fuck up
b) go the fuck away
c) go annoy the fuck out of someone else
d) an all inclusive phrase of general distaste which includes a-c as well

A stupid person; it refers to the lack of surface area on an individual's brain. The general thought is that the more surface area (wrinkles, creases, etc.) a brain has, the smarter the person is. Conversely, a person with a smooth brain (no wrinkles) has less surface area and would therefore be stupid.

When someone tells you to go fuck yourself, they are encouraging you to shove your penis up your own asshole by bending it backwards. Or, if you're a female, to grab the nearest phallic object(s) and penetrate your orifices repeatedly. The connotation is that you'll probably enjoy it and will stop annoying everyone.

Basically, means to just for the person to stop everything he/she is doing and find the nearest gun, point it under their chin and pull the trigger. That way they will no longer bother you and you can get some peace and quiet without their pure bullshit spewing from their mouths. If one continues you to harass you after you say this, you legally have the right to make them discover what your fist tastes like. They cannot sue you for any reason.

A command uttered usually after one has said something infuriating or offensive to you.

To tell someone to go away or to just leave you alone or never talk to them ever again.

A command for someone to get lost (especially from the person that says it), usually as a result of extreme annoyance. Literally it means for them to masturbate themselves, so they aren't inclined to harrass and receive sexual pleasure from the person they are annoying. It's more stinging than "fuck off" because it implies that they could not or should not find anyone else to have sex with, so they need to use the self-manipulation.