Twopence ha'penny millionaire

[Ernesto]

A person who pretends to have millions of pounds in the bank, but actually struggles to find a penny to scratch their ass with (A twopence [halfpenny] is the equivalent of [pound sterling] 2.5pence).
Usually walks around in fake designer clothes/clutching an imitation designer bag. Alternatively, they may have one genuine designer item with which they parade around with consistently. Can also apply to people who emphasise what they actually do have, or lie about what they have e.g. the size of their home/their earnings/the make of their car.
If being extremely stereotypical, it would be accurate to say that twopence [hapenny] millionaires are usually insecure and rely on this behaviour to get attention or gain some credibility.