In English the word "creep" means a detestable suspicious person. The word "real" in this case is used as an emphasis, so adding "real" to "creep" would mean the same as writing both "very big creep" or closer to "actual creep", used as emphasis to describe someone who fits the definition of the word perfectly.

'to creep' is a verb to describe vicious and fishy movements, but it is usually used metaphorically (as a noun) to describe a disgusting person whom you cannot trust. Ex: There is a creep who keeps stalking me every time i get out of the office. some other synonym for its metaphorical use are: -bastard -beast -jerk -weirdo