Go on to gatecrash very pathetic party (5)
I believe the answer is:
saddo
'pathetic party' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.
'go on to gatecrash very' is the wordplay.
'go on' becomes 'add' (I've seen this in another clue).
'to gatecrash' indicates putting letters inside (inserted letters gatecrash their way in).
'very' becomes 'so' (both can mean 'extremely').
'add' placed within 'so' is 'SADDO'.
Can you help me to learn more?
(Other definitions for saddo that I've seen before include "pathetic person" , "He's pathetic!" , "lonely person" , "Boring loner" , "loser" .)