Straight students primarily drink pop (4-4)
I believe the answer is:
slap-bang
'straight' is the definition.
Both the definition and answer are adverbs. Perhaps they are linked in a way I don't understand?
'students primarily drink pop' is the wordplay.
'primarily' says to take the initial letters.
'drink' becomes 'lap' (to lap is to drink up).
'pop' becomes 'bang' (I can't explain this - if you can you should give a lot more credence to this answer).
The first letter of 'students' is 's'.
's'+'lap'+'bang'='SLAP-BANG'
Can you help me to learn more?
(Other definitions for slap-bang that I've seen before include "Suddenly - directly" , "All at once - violently" , "right?" , "Absolutely (in the middle)" .)