If you want to comment with an Imgflip Chart or Demotivational, you have to make one of those first, download them, then copy paste the image into a meme comment, OR make them first and use the "share" button to get a "click to show" link.
The only option for a gif comment is a "click to show" which is a bit cumbersome these days, since they did away with the BBCode option in the "share" button.