I never call somebody out for not calling a hit, just shoot them more in a different spot.
Everybody is getting more and more gear to complete a look they are going for, and this means that there are more and more spots that you can hit them and they will not feel it. If they have some fancy headset or are in a fire fight, they might not hear the hit either.
I always give other player then benefit of the doubt (unless I can obviously tell that they are ignoring hits) because I am sure that there have been times where I was caught up in a moment, listening to radio chatter all mixed in with the noise of a running mechbox or GBBR, and I have not felt or heard a BB hit my gear.
Its unfortunate, but it cannot be helped.