All banjo jokes should be reassigned to melodeons but here's one anyway:

Melodeon player working on building site stops for lunch. Opens lunch box and shouts " Not ham sandwiches again - if I get ham sandwiches again I'll kill myself"
Next day - lunch time - opens box - ham sandwiches - throws himself under the nearest bus and is killed.
Some days later at funeral - wife says to mourners " I really can't understand why he did it - he always makes his own sandwiches"
Longer version also available.