Noun. Making someone "Eat it" is the act of pushing an object (for example, a handful of bark, or a pie.) into their face (aiming for the mouth) while yelling in a high pitched voice "Eaaaaaaat iiiitttt!". This is often practiced when someone may be rambling, or as an act of revenge. Such an act can either be seen as hilarious, or downright immature, depending on the circumstances.
This can also be done as a joke to friends, where the object may not actually touch the face, or very gently. Another variation of eat it is the act of pulling someone's face into one's crotch, while yelling "Eaaaat itt!" though in a very low pitched voice.
Past tense - Ate it.
"John made Jason eat a bit of meat pie on a stick, so Jason opened his pizza rounda and made John eat it."
"I'm gonna make you eat it if you don't shut up."
"EAAAAAT ITT!!! You just ate it. Bad."