From Now On You Can Call Me The Anti-ultracrepidarian
adjective 1. noting or pertaining to a person who criticizes, judges, or gives advice outside the area of his or her expertise: The play provides a classic, simplistic portrayal of an ultracrepidarian mother-in-law.
1800–20; ultra- + Latin crepidam ‘sole of a shoe, sandal’ (< Greek krepis ‘shoe’); in allusion to the words of Pliny the Elder ne supra crepidam sutor judicare ‘let the cobbler not judge above the sandal’; cf. the English proverb “let the cobbler stick to his last”.
With thanks to Alastair Roberts for telling me about this delightful word which perfectly summarizes the concept of dilettantism.