What lovers do in luxury car is tops (4-5)

I believe the answer is:

roll-necks

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'what lovers do' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.

'in luxury car is tops' is the wordplay.
'in' means one lot of letters goes inside another.
'luxury car' becomes 'Rolls' (Rolls Royce).
'is tops' becomes 'neck' (I can't explain this - if you can you should believe this answer much more).
'rolls' placed around 'neck' is 'ROLL-NECKS'.

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