Sandra Bullock is suing a watchmaker for using her name in ads without permission.
Using a celebritiy’s name (or even a photo) without permission for commercial purposes can lead to a serious lawsuit, especially as many celebrities live in California and California law provides for robust protection of the Right of Publicity.
But even non-celebrities can sue under their right to privacy if you use their face or name without permission in your own movie.
Generally, you should always get a release from anyone you videotape or film. Also, have your script vetted by an entertainment attorney before you shoot! And save yourself some trouble.