if you want to use it as DIRECT OPENER then you can go like..
i can be your shakeweight only if you promise to be gentle...
[actually WINK, and done with a little smirky naughty look on your face.]An ULTRA-SEXUAL OPENER would be ==
i can be your shake-weight if you like shaking things which are heavy..
OR, to ask it as a QUESTION - OPENER,
i can be your shake-weight but dont really know if u r strong enough... Are u strong enough..??
OR, to generate an INDIRECT OPENER out of this.. go like --
i can be your shake-weight, but you might have to earn that...can u tell me where the nearest starbucks isss...??
OR, to create an OPINION OPENER out of this... say --
i can be your shake-weight, but i am not really sure if girls like you prefer using shakeweight over ardous gym-workouts.. what do you think about it...?
-- To a response for this.. the girl would either get stuck at the "girls like you" part and ask you == What do you mean girls like me..blah blah..?? or she would take the bait and get absorbed by the question about the workout preference...!!
