1.
A looser is a loser who can't spell "loser".
Moron: "Hey man, you are teh looser!"
Guy: "It's spelled 'loser' you uneducated bastard."

2.
Maybe the most common loserish misspelling of loser.
Me: Loosers are losers.

3.
Idiotic way of spelling "loser". Most often used by teens and adults with no more than a 2nd grade grammar level.
Guy 1: OMG! Todd is such a looser!
Guy 2: I told myself I was going to do this do the next person I saw spelling the word "loser" like that; so now I am going to set your house on fire. You brought this upon yourself.

4.
Loose taken to the next level, or 'more loose'.
1) Sometimes it's just not good enough to be plain loose. You need to be looser.
2) Michael was looser than Shelly.

http://www.urbandictionary.com/define.php?term=looser