pack of galahs
A pack of galahs is a bunch of clueless twerps who think they know everything but are really just a load of useless shits.
My boss is a pack of galahs. He can't even make coffee properly.
That group of galahs at the office party talked non-stop about their kids' spelling tests.
My sister's friends are a pack of galahs. They all think they're the best at everything.