Threatening behaviour (5)

I believe the answer is:
aggro
'threatening behaviour' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for aggro that I've seen before include "In slang, hassle or troublemaking" , "Difficulties (slang)" , "Bovver!" , "Slang for deliberate trouble-making" , "offensive behaviour" .)