A choo-choo nigga is a group of dark skinned (ie. black) people who like to dance the conga in the street. Especially common in Palma de Mallorca, where daily choo-choo niggas walk the streets singing and dancing to their ryhtms.
This is the music prefered by choo-choo niggas "Choo-choo-choo, cummon and do the conga!",