Disregard dope times on bit of phencyclidine (4,2)
I believe the answer is:
pass by
'disregard' is the definition.
(thesaurus)
'dope times on bit of phencyclidine' is the wordplay.
'dope' becomes 'ass' (both can mean a stupid person).
'times' becomes 'by' (both can mean 'multiplied by').
'on' means one lot of letters go next to another.
'bit of' indicates taking the first letters.
The first letter of 'phencyclidine' is 'p'.
'ass'+'by'='assby'
'assby' after 'p' is 'PASS BY'.
(Other definitions for pass by that I've seen before include "Go on and leave alone" , "Leave on one side" , "Move along in the vicinity" , "Overlook; go beyond" , "neglect" .)