religion which became laws.
mistakes which became lessons.
experiences which became knowledge.
and the rarest of them all: common sense.
It doesn't matter what you and I believe or not believe in, what matters is: DOES IT MAKE SENSE?
All this combined brings Karma.
what you did, do and will do defines your situation may it be what happened in your past, what is currently happening, or what will happen in your future.
That is why you must always give others the benefit of a doubt.
Always ask why they behave that way.
They may rub you as "bigot, racist, douchbag" etc but remember that it is the reason why they are that matters.
if it is a lowly reason, then simply treat them horrendously until they understand that it is because of their attitude why they are treated that way.