Is flirting ok with your family ?? I don't think it is ....! =(?

Ok heres the deal .....my sister has been married for almost two years ...to .well lets just call him Bob ....and Bob is a nice guy he treats my sister and her kids good ...and he's very nice ..but lately I have been feeling uncomfortable around him ...cuz he flirts a lot ..like I don't think he really knows he is doing it ....for instance when I see them ....he will be like " hey y " or " wow you look really y " or " is that a new shirt ..its cute " and he notices when I get a new hair cut ..and will be like " oh that looks realli nice on you " and I know what you guys are gonna start thinking ..oh yah he's a perv ..but he's not .....its not like he has ever made a move on me ..and he always tell my sister he loves her . But I don't want him talking to me like a guy who likes me would ..all that flatering stuff . He is not always telling me how good I look he flirts in other ways .....like we will though little pebbles at eachother and three went down my shirt on time and