Taken from the urbandictionary definition of "forrest":
"Although commonly thought to be derived from the English word 'forest' which is a "large woody area," it is actually the reverse. It was a name, 'Forrest', first with an ancient Greek translation of "Large Penis." When looking for a name for a "large woody area," the English adapted what they already knew had "large wood," to the slightly altered spelling, 'forest.' Basically, Forrest is a name for a person with a huge dick."
But infact, the above quotation is wrong. The word "forrest" was mispelled and was meant to be "forrestt". Forrestt is all of the above and more. Generally a Forrestt sucks major ass at first person shooter games such as Call of Duty: Modern Warfare 2, with the exception of the Halo series, in which they generally kick ass.
X: Dude! That guy was hung like a Forrestt!
Y: Yeah I know!
X: Looks like we have a Forrestt on our team. /facepalm
Y: Oh shit look out he's noob tubing /facepalm
X: Hell yeah! We have a Forrestt on our team!
Y: W00T nao i dont hav 2 uze mi hax 2 kik covnent arse!