A cainer is a british slang term for a person who likes to cain (take drugs, smoke weed, drink alchohol)
The word cain
can mean to indulge in something to a rather extreme extent. This particularly relates to the 'caining' of drugs, alchohol and marijuana.
"That fuck heads a right cainer"
"My mate Daveo cained all of the coke"
"Alright cainer, shall we get hammered
"That greeny lads a right cainer."
a fast driver, someone who drives responsibly yet as fast as the conditions will safely allow, in other words a pistonhead pistonheads
TrafPol, car enthusiasts (some exceptions),
drinking lots, smoking lots generally doing things to the extreme....
person 1: I was so cained last night...
person 2: you certainly were my friend, you cainer you