In a pinch, you get too lazy to open GIMP or ComiPo or your lavish Adobe CC, and you Google search for a web app to do flop 1 image unto 1 other image? Overlap Overlay...
This is handy as well.
Web app in link ^
It could use more options, but for quick sake, you already got GIMP or Paint for full Ui meme making. It's my goal for future tho.