Okay, Hoi Polloi is actually two words, but they go together so tightly that you need both to make sense of the phrase. This is a phrase what we hope many are not aware of and even more do not use.
Hoi Polloi is a derogatory reference to the “common people,” the “huddled masses.” It refers to those of us that are looked down on by elitist who consider themselves to be above the “common people.” The term hoi polloi is derived from Greek meaning “the masses,” also referred to as the “huddled masses” or “the great unwashed.” Another derogatory synonym would be “riffraff.”
In everyday use “hoi polloi” might be used in sentences:
From her penthouse suite she looked down at the hoi polloi below and felt sorry for them.
In 1929, the hoi polloi had no jobs and had to line up for bread and soup on the sidewalks.
It was clear that the ultra-rich lived in their own estates and did not associate with the hoi polloi.
“Prolly” is so bad that we cannot call it a contraction, or a misspelling, or anything but bad grammar. When someone uses “prolly” they are using a slang term for “probably.”
Are you going out tonight to dinner? Response: Probably, not “prolly.”
Do you think Sally is taller than Jane? Response: Probably, not “prolly.”
You prolly know his name already. [cringe!]
I am prolly the last person you should ask. [cringe!]