VineGifR requires only a valid Vine link to turn the short video into a GIF. Once you have the link, you enter it into the only text field in the app and click on "GIF'it." You'll be asked where to save the GIF and to give it a name. The end result is a GIF similar to the one below:
Since the app only requires a Vine URL and Vine itself doesn't offer any type of privacy settings, this leaves any Vine video ripe for conversion. Just be sure to ask permission and all that good stuff before you go creating GIFs out of Vines that don't belong to you.