1. A vulgar expression to depict the action of thrusting the penis into the vagina. Mainly used in the company of "Lads"; this phrase carries an air of Bravado about it.
2. Can also be used when describing a young lady who might not be up to ones usual standards aesthetically but would be adequate for the purposes of short-term sexual gratification.
3. Used in a jocular manner when performing everyday tasks. By simply emphasising the words, a very humorous effect can be achieved. ie When inserting a floppy disk into a computer.
"Stick it in, Derek!"
"I'd stick it in!"
"Have you been sticking it in?"
"You didn't stick it in did you?"
"Just take this disk and STICK IT IN!"