Ya gotta see the video, J Lo played it perfectly ... as Ben pulled into the driveway Thursday, she rushes up to the car, throws her arms around his shoulders and starts making out with him. Ben even seemed kinda shocked, but quickly got into it.

Jen leaned back on the car and pulled her fiancé in close, rubbing his chest, planting more kisses and staring into Ben's eyes. If you have any doubts they were playing this up for the cameras ... check out the moment BA goes into full movie make-out mode.

We're not saying the sparks aren't real for the recently engaged couple -- we're just saying they went over the top here ... intentionally, we're thinking. They're both pros in the PR game by now, and know what catches fire on the internet.'

Jen even playfully sticks out her tongue at Ben as she hops in the driver's seat.

This make-out sesh must have felt almost as good as sex ... because Ben lit up a cigarette right after Jen left.