Her Dad Grabbing his Daughter Tits

Me and my daughter don't get on since she started to developed we fight like cats, she has always been her dads girl
even though she has grown up she still sits on his knee, what I don't like and it really bothers me is, he will go up behind her and grabbing and squeezing her tits and makes comments like these are growing nicely, he frequently passes comments on them saying what I good pair, she doesn't wear a bra at home,
Should I say something knowing what a row it will cause if I chastise her they both argue against me, I know daughters are special to there dad, could something more be happening, or is it just fun, she doesn't seem bothered at all