If you say kewl (seriously and not for some sad irony,) you probably also say "u," "r," "stpd" and stuff like that, and blame it on the fact you want to type faster. If you had a brain, which by this point most people will have worked out you haven't, you'd realise typing kewl is slower than typing cool and is also that you'd learn to type faster if you actually typed whole words.
It'd be nice if noobs would note not to say this word around people with a brain, because it works a little like passive smoking. :(
"lol d00d! thats fkn kewl!! lol"
"stfu ur not kewl" (thank fuck for that)
Probably copied by random people who thinks it's pronounced 'cool' and then used it as if it meant 'cool'.
Later, people got annoyed of it and made themselves look like shitheads by defining it on Urbandictionary.com. The same people later gave this defination a thumb down because they felt offensed by it.
And even later, this defination got deleted and no one could read it any longer. But by then, no one cared.
Yes, I'm lazy.