esmi was a result of a drunken conversation on IGN.
Like many other nerd/1337 words, it came from a spelling error.
"esmi" is a mispelled "semi".
Often used instead of "owned", "pwned", "own3d", etc. which often is a variation of dominated, defeated, crushed, or proven wrong.
1) leik LOLOLOL, that bitch got esmi'd
2) WTF, my computer wont start up!