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 don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'in luxury car is tops' is the wordplay.
'in' indicates putting letters inside.
'luxury car' becomes 'Rolls' (Rolls Royce).
'is tops' becomes 'neck' (I can't justify this - if you can you should believe this answer much more).
'rolls' enclosing 'neck' is 'ROLL-NECKS'.

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