suffenous
Originally coined by the ancient Roman poet Catullus in poem XXII from the Latin adjective "suffenum". It can be translated as meaning someone who spends a lot of money on new hobbies, enjoys them, fancies themselves good, but is sadly oblivious to the fact that they suck.
Iya's brother's attempts at playing the guitar sound suffenous to me. Every six months he will get a new hobby, spend all his money on it, practice a lot, but still suck.