Well if he want's you to be a slut around his friends too then that would probably mean a lot of flirting with them. i would say do things like bending over to pick things up with your ass or breasts in thier face, make inuendos around them but then look at your Dom in the eye to show him that you like turning on his friends but are just meant for him. Make it a point to do a lot of touching or petting of his friends when they are around. Do it to your Dom too when his friends are watching. It sounds like he wants to show you off to his friends, show that he has control over your sexual desire. He may also want you to do this just so you can be naughty and he has reason to punish you.