Rather than show a pop-up when you try to vote your own question or answer up or down, just don't show the vote buttons - much like how there's no upvote button on your own comments.
Yes this is a great idea then we just have to update out FAQ with this that
You can't upvote your own post even it is answer or question
Or community can point out with a separate FAQ like
Why I'm unable to see the Vote button on my own post while others posts I can?
and the answer could be more powerful then mine
You can't vote to your own post so you are not able to see those buttons for your own posts.