Quote: Chappers @ 1st October 2014, 10:16 PM BSTDid you post it to yourself?
You should say "I shouldn't have asked them to post it to me by Royal Mail".
For the actual flow of the joke I personally prefer the more pithy version. I think 'shouldn't have used royal mail' can also be understood as 'choosing Royal mail as the postage option.'
As for the cat one, cats aren't vegetarians, so getting rid of them nominally would please vegetarians, except if you actually went hunting cats you may just find yourself extremely unpopular with them. As to the hashtag, that was something I genuinely noticed