What do you do when people poke you irl?

Some of my acquaintances (my close friends have never poked me) for some reason like to poke me in my side & stomach and honestly it annoys me but I don't say anything because I don't want to be rude or make it more awkward. It makes me uncomfortable being poked 'cause idk what to do, 'cause either I sit there w/ a fake stupid smile on my face or I poke them back and then it turns into some dumb stupid poke war that I would've rather not taken part of.