snub
To purposely ignore someone to make them feel unimportant.
To snub someone means to deliberately ignore them or treat them as unimportant, usually in a way that's obvious and hurtful. When you snub someone, you might walk right past them without saying hello, leave them out of a group activity on purpose, or act like they don't exist when they try to talk to you.
The word carries a sharp sting because a snub isn't accidental. If you don't notice someone waving at you because you're focused on your book, that's not a snub. But if you see a classmate trying to join your lunch table and you deliberately turn away or pretend not to notice, that's a snub. People snub others to show they're angry, to assert social power, or to make someone feel excluded.
Being snubbed hurts because it's a form of rejection. Imagine working hard on a science project and having the teacher completely ignore your raised hand while calling on everyone else. That feeling of being intentionally overlooked is what makes a snub different from simply being forgotten.
As a noun, a snub is the act itself: “She felt the snub when her supposed friends didn't invite her to the party.”