I've got two problems with this. One is the idea of asking an adult to control the behavior of another adult -- especially a parent. I think a better alternative would be, "Hey, can you let your dad know my folks are kind of uptight, so I'd appreciate it if he watches his language when he meets them?"
The other is that asking dad to modify his behavior = asking dad to "not be himself." We all modify our behavior depending on the situation we're in -- workplace, locker room, church. You can refrain from insults and off-color jokes in a given situation without sacrificing your very identity.