Why do people like to touch my pregnant tummy? How do I tell them not to?

They are probably excited to meet your little one and want to say hello! The best way is to simply telling them straight (but politely) that you are not comfortable with people touching you (people often forget that your bump is a part of your body as well). Or you can try a nonverbal approach by putting your hands on your bump (to signal that you do not welcome their advances) or turning your body (slightly) away from them as they approach you. For people whom you are closer to, you can even try reaching out to their tummies as they reach for yours. Perhaps, then, they will understand how uncomfortable it is for you.