yo man dont worry i got the best way to do this cuz i did it 2 years ago man so if ur just driving around with him jsut bring it up be like so u wanna go smoke a blunt and if ur dad is cool he will be like haha funny and jsut be like ims erious and then let it go like that u kno and jsut keep doing that like ur joking but be like ims erious at the end and jsut be quite so like if u r watching a game or somthing jsut be like HLAF TIME lets go smoke a J and eventualy if ur dad is cool jsut bring it up like intensly after doing that and u will know or if ur lucky he will be like aight whitch rarly happens so dont look foward to it