When you don't respond to someone, you are ignoring that person. When you ignore someone, it is rudeness. Be kind, not rude.
When someone messages you or calls you, or wants to meet you, have the courtesy to at least respond. You may choose to ignore only your enemies for strategic reasons, not anyone else. Ignoring anyone else is downright rudeness. Your negative karma you have caused by hurting someone by not responding will come straight back at you. You will be hurt at a future date. It's guaranteed.
Don't be rude. Ignorance is rudeness.