Accidentally left apartment house without top hat and fake ID (8)
I believe the answer is:
username
'accidentally left apartment house without top hat' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.
'fake id' is the wordplay.
'fake' becomes 'user' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'id' becomes 'name' (I've seen this in another clue).
'user'+'name'='USERNAME'
'and' is the link.
Can you help me to learn more?
(Other definitions for username that I've seen before include "Something needed for logging in" , "Computer log-in requirement" , "Online identity" , "One's identifier on a computer" , "Login ID" .)