Your Karma is defined by your Actions plus your Intent. A seemingly incorrect action with a pure intent can potentially result in good Karma

He insulted me’ -this knowledge binds one with terrible demerit karma.

If Karma is a thing, then wouldn’t wanting someone to experience bad Karma also get YOU bad Karma?

Calculate your karma before your actions

A person gets the people around oneself not by own desire or wish, but as who s/he character-wise is. That's perhaps the first cardinal rule of Karma.

The consequences of our actions take hold of us quite indifferent to our claim that meanwhile we have "improved".