Junkie knocked over drug dealer for PC Handle (8)
I believe the answer is:
username
'pc handle' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.
'junkie knocked over drug dealer for' is the wordplay.
'junkie' becomes 'user' (I've seen this before).
'knocked over' shows that the letters should be reversed in order.
'drug' becomes 'e' (E is another name for ecstasy).
'dealer for' becomes 'man' (I can't justify this - if you can you should believe this answer much more).
'e'+'man'='eman'
'eman' back-to-front is 'name'.
'user'+'name'='USERNAME'
Can you help me to learn more?
(Other definitions for username that I've seen before include "One's identifier on a computer" , "Electronic identity" , "Log in identifier" , "Person's computer ID" , "Online identity" .)