faux posh
an embarrassingly tactless person who acts and speaks as though they are significantly more high-class than they really are.
"Simon speaks so eloquently and with such great articulation. He wears those weird shirts with elbow patches, too... He seems to be really posh."

"Simon? Posh? Ha! No... He grew up just as poor as we did. He just became faux posh when he got the gig on that YouTube channel."