originally used as a normal word in phrases such as "we win the championship" "I will win this trophy" etc. But since the rise of
online gaming, it has been used more and more
out of context, and has developed into a nerd slang term.
Instead of using proper grammar, these geeks say "win" every time they see
something funny or amusing. (See example).
I do not know how this is a "cool" word, but like I previously said, it's nerd lingo.