Gif Central boasts hundreds of funny animated gifs. Only the best of the best make it onto this site, with most of them having an accompanying source. No tumblr-esque one-second-long disappointments. No obscure titles or descriptions.
This is an animated gif of Commodus from "Gladiator" (played by Joaquin Phoenix) giving a thumbs down. This can be used as a reaction for whenever somebody says or posts something that you disapprove of.