I poured oil over my elderly neighbor's porch to make it slippery
Are you trying to get your neighbor hurt? Did they fall?
Yes, they did. They suffered minor injuries
Hurting others on purpose is completely unjustified. Your neighbor may be rude or kind, but your actions do not make anything correct. Apologize to them and offer to clean up their porch.
If they are mean to me I'll do it again.
Sabotaging someone is a possible crime and elderly abuse. If you can't stand them there are other civil things you can do like call a wellness check.