1) someone who make others confused especially by talking.
2) any drug that prevents you from thinking.
3) something that is hard to understand.
1) - i had some plans but i don't know what to do now.
- you shouldn't have talked to him. he's a brainkiller.
2) i remember nothing about the accident. are you sure this drug is a painkiller instead of a brainkiller?
3) all the calculation is a brainkiller for me.