Video copyrights and GIFs. If i take some cells from a movie & make a GIF, how much can i show & remain legal?

I have heard some on some TV shows, they can sometimes only show about 3 seconds of a movie to avoid copyright infringement. I want to make GIFs from movies (like a looping slow-mo punch to the face). They usually only last a few seconds, and considering its only using a few cells from the movie, its not even close to 3 seconds of 'real time' video. I am only using this for forum avatars and personal use, no money exchanges at all, only for fun, but posted various places on the internet. You think I can do this without any harrment? Would that be considered 'fair use'?