To poke someone in the belly while simultaneously saying the word "bumph" when they don't expect it. You can also add the phrase "Did that hurt?" after the bumph has been issued. It is not necessary but adds a significant effect to the bumph. Sometimes the bumpher will bumph you back and at that point, the only proper way is to bumph back leading to a bumph war. During a bumph war, the bumpher may add in some more phrases such as, "You ate the dirty grapes!!" or "Her hair, its so short!" while the person getting bumphed responds with, "Pheeeeasant foooooot" or "Ouch! DAT HURT!!"
Lisa: "Bumph! Did that hurt?"
Tom: "Ouch! Stop it! that hurt. Bumph!!"
Lisa: "Bumph, you ate the dirty grapes!"
Tom: "No you did! Your hair.......its sooooo short!"
Lisa: "OHHHHH goddddd, Bumph"
Tom: "Pheeeeasant foooooot"
Lisa: "Once you name it......"
Tom: "You get attached to it!"