[Cobra64]

Actually, Jimmah, it was prolly worse when the bullets were flying....

What is a "prolly?" Is that a kid's rap term?

[ilovesarah2012]

It’s southern for “probably”. Kind of like “supposeably”. LOL

[StormEye]

"What is a "prolly?" Is that a kid's rap term? "

It's a substitute for the word "probably."
Why do people use the ridiculous non-word "prolly"?

1) They don't know of the word "probably" and how to use it.
2) They don't how to spell the word "probably" so they don't use it.
3)They think they are being cool or cute in a literary way and that will impress someone.
4) They are too lazy to spell the word "probably".

Those are my guesses.