You might think Jam-ooh! is phonetic for his english last name but you are already wrong and it’s just the first sentence.
And no it’s not because he has a large colletion of Jimmy Jam albums on vinyl in vacuum sealed plastic sleeves.
And no it’s not because he likes to say “Jam” when he is talking about nocturnal activities that, frankly he probalby hasn’t really experienced.
And no it’s not because he’s a maestro on the six string anything, because he’s not.
And no it’s not because he tastes jellies like they are wine vintages, because he’s tasteless.
So actually we just don’t know why they call him Jam-ooh! And we really don’t care.