This does not work with people with counters you can`t get behind. First, enter the hairstyle menu (this is not neccesary with the other owners). Next, just exit the Menu. Now, go up to the barber and do a running jump. This will make them angry and try to attack you without you getting kicked out of the store. If you attack them back you get kicked out of the store. So basically, you just get pounded on by the owner. Have fun!