This PC has made himself and the force a laughing stock.
Without wishing to be ageist, this was an elderly man who had had two strokes. Even if the white stick wasn't a huge clue that he was also blind, he was no threat to this Police Officer, he wasn't likely to be running away. Surely there are rules about how tazers can be used and this must have broken several of those rules. If it was used legally, then the rules must be changed with the upmost urgency.