Snap at them once, leave a good impression, they will never do it again.
say Ouch loudly. they will get embarassed, if the day,"sorry, did that hurt?" say, "no, not at all, I was on local anesthesia, why don't you try again !?"
You shouldn't stop being polite, you just need to work on being more assertive. Getting mad and being aggressive isn't any better than being a doormat.
Make it look like they didn't bother you.
both work when used correctly.
dont put up with these peeps or you'll find yourself covered in footprints