If you flinch whenever you hear someone address a group as "youse", consider that it's you, not the speaker, who's the uneducated, ignorant one.
Are you still there? Great! Now let me tell you why this is so.
In standard English, you is both singular and plural. While that may seem unremarkable to you (that’s you sitting in your seat, and all of you collectively), it separates English from many other languages that do distinguish the singular and plural forms.
It also distinguishes standard English from its many non-standard forms. “Hey youse!” is a perfectly sensible way for the speaker to make it clear that he’s addressing the whole group, not just one person. Likewise with “y’all”, “youse guys” (New York mainly) and “yinz” (Pennsylvania).
It also makes the speaker more consistent than everyone else. Standard English already distinguishes between I and we, and between him/her and them. You is the only personal pronoun with just the one form for both singular and plural. But having a separate form for each would be useful, no?
In fact, we once did. Early English had thou, singular, and ye, plural (hence "hear ye, hear ye"). After the Norman invasion, thou gradually became a familiar form of address, and you a formal, deferential option. So if you were chatting with the king, he’d say “Would thou like a bowl of maggot-infested gruel?” and you would grovellingly reply “If it pleases you, Your Majesty”.
Then, around the 18th century, thou began to fall out of favour. The reasons are not entirely clear, but some commentators invoke an emerging spirit of egalitarianism.
Either way, that left you to do the heavy lifting for both singular and plural references. And the so-called uneducated masses to do something about it by newly inventing plural versions. Good for them, I say, the clever Dicks.
Youse may not be standard English, but it's certainly neat, clean and logical. You don’t have to like it, but heaping scorn on it is both illogical and unjust.