another man slapping me

so theres this friend i have who has slapped me on my ass a few times, im a guy and this is another guy whos doing it to me, at first i felt really awkward, like dis he really hit my ass????......kinda made me feel violated in a way. but this last time was tonight. and i dont know what to think now. is this a sign hes into me sexually or????....ill admit it did kinda turn me on. im straight but since hes been doing it to me i feel somewhat different. im not sure how to approch this because i dont want to make him feel someway.....i just need some help. any ideas?.....what should i do?