knucklehead
macrumors 6502a
Long press on the GIF and select "Save image" then it saves it to the gallery. Then to post it you can use an app like Tapatalk.
Random one I just found on the net:
View attachment 398781
Same for saving things like photos in email. I don't have a video in an email to test like was stated a few posts up, but I suspect that would work too.