Theoretically, the Liverpudlian term 'scally' is a young boy who lives in a lower class neighbourhood and has a low paid job (if any at all). He will usually dress in dirty tracksuits, skin-headed with baseball cap, and worn trainers. Scallies are normally seen in a gang, which they loiter around sports shops, amusement arcades and fast food restaurants looking for a fight or something to steal.
However, for some unknown reason, this 'rude boys' image of scally is kinda BIG in the gay community and it seems like it's one of the most recent variants on the ever-popular 'bit-of-rough' for those who have the preference. Maybe you don't agree with me, but you should at least watch this clip above and see if he can convince you. Enjoy!