There are two interconnected meanings from this word: an adjective and a noun as follows;
1. the loose piece of skin on the under-belly of a man's penis, stretching from just before the 'bell-end' upto the scrotum sack.
2. the act of gripping the aforementioned ragalag between the thumb and fore-finger and gently shaking it, i.e 'ragalag-ing'. This is often done in the presence of a girl to promote the feeling of digust.
Cant think of one