1) It's a Slide LOCK, NOT A SLIDE RELEASE. Just because some Hollywood Moron does something in a movie it doesn't mean that is the proper way to handle a firearm. With many semi autos thumbing the Slide Lock to release the slide will cause enough wear over time to cause the Slide Lock to not function properly.

2) To slingshot a slide you pull it all the way to the rear and RELEASE the slide. This means you simply LET GO. As in OPEN YOUR HAND AND ALLOW IT TO SLAM FORWARD. Sort of the way you would use a SLINGSHOT. BTW, it's a handgun, not a Ming Vase, and allowing the slide to slam forward won't cause any real harm unless you make a habit of doing this 1000 times a day. Technically with some semi's dropping the slide on an empty chamber can increase the impact of the slide closing and possibly cause a small amount of wear on the recess that locks the barrel into the slide. Because of this it's advised to only drop the slide when you are actually loading a round into the chamber. However an occasional test to confirm function would likely take several hundreds of years before any excessive wear would be noticed.