The 22-year-old singer said that he picked up the nickname after his fellow group members saw him naked after a concert.
Merrygold told the Daily Star: "We normally jump straight into the showers after a show. I jumped out naked and was waving my bum at the lads, messing about.
"They've nicknamed me 'Skinny Bum' ever since. They won't stop calling me it."
He added: "We call Oritse 'Hancock' because of his superhero-sized willy, Marvin 'Incredible Hulk' because of his big muscles and JB 'Bananaman' because [his group colour is] yellow."
heard there was a secret chord
that david played and it pleased the lord
but you don't really care for music, do you
well it goes like this the fourth, the fifth
the minor fall and the major lift
the baffled king composing hallelujah
hallelujah...
well your faith was strong but you needed proof
you saw her bathing on the roof
her beauty and the moonlight overthrew you
she tied you to her kitchen chair
she broke your throne and she cut your hair
and from your lips she drew the hallelujah
hallelujah...
baby i've been here before
i've seen this room and i've walked this floor
i used to live alone before i knew you
i've seen your flag on the marble arch
but love is not a victory march
it's a cold and it's a broken hallelujah
hallelujah...
that david played and it pleased the lord
but you don't really care for music, do you
well it goes like this the fourth, the fifth
the minor fall and the major lift
the baffled king composing hallelujah
hallelujah...
well your faith was strong but you needed proof
you saw her bathing on the roof
her beauty and the moonlight overthrew you
she tied you to her kitchen chair
she broke your throne and she cut your hair
and from your lips she drew the hallelujah
hallelujah...
baby i've been here before
i've seen this room and i've walked this floor
i used to live alone before i knew you
i've seen your flag on the marble arch
but love is not a victory march
it's a cold and it's a broken hallelujah
hallelujah...
