a term often heard in northern ireland,it means the effects of consuming copious quantities of ecstacy or MDMA. the afflicted person's eyes will roll back in their skull,the jaw will move up and down at approximately 93 mph,and the words "man i am soooo baked" will usually be spoken in an unintelligible manner.
Derived from the word wallop, which is onomatopoeia (a sound word) for an impact of some sort, it is a Scottish slang term for a penis, usually a large penis.
It is also used to refer to unpleasant people, much like dick, cock, prick and knob would be used in conversation.
"Jesus Christ, did ye see the size of that walloper he had on him?"
or
"He's a bleedin' walloper, and that's all there is to it!'