My dad keeps on touching my bum. What shall I do?

I didn't see my dad for 15 years when I was growing up, but when I was 19 I decided to get in touch with him. I am now 25 and although my dad is really lovely, he keeps on putting his hand on my bum. I have said in the past "please don't put your hand there" or I make it quite obvoius by moving away. The other day I was standing in his kitchen and he slid his hand down to my bum and I gave him a really hard "playful" kick when he did it. I feel that because I did not grow up with him, physical barriers had to be broken (like even giving a cuddle) and bum touching, even if it is just affectionate, is way off the radar. Am I just being really uptight? Or is that completely innapropriate? I can never tell if it's affectionate contact or he's just being a complete pervert. What do you think?