purp, there aint nothin wrong with saying "prolly"
It's our California accent. If you want us to use proper grammar and make a feeble attempt to impress you with our extended vocabulary, go read one of my college papers.
i find no reason to need to have to spell the world "probably" correctly. prolly just cuz its easier and more convenient, and im used to it. if some stranger from the internet was being rude to me about it, that wouldnt make me want to change up my typing and/or texting habits. just run with it
light one up, ease up bud. we're all family here
(of course thats unless you're underage
punk ass kid haha)