Firstly let me state this is not an original idea – recently a Beer Bottle Lock made the rounds on 3D printing news sites, stemming from an Instructables tutorial by JON-A-TRON (see http://www.instructables.com/id/Beer-Bottle-Lock/ for the original).
However with Xmas fast approaching I wanted to design one for a bit of fun with my family. Simply print the 2 pieces out and use any small travel lock to secure that final beer (whether it's yours or someone else's!). Unlike the original by JON-A-TRON this design requires no screw. The dimensions are quite loose so that it should securely fit a wide variety of bottle shapes, if you don’t need this flexibility you might like to thicken 1 or 2 areas on the inside prior to printing.
Sure it's could be snapped off, but this design is really just for a bit of fun - if you're genuinely worried about people stealing beer maybe you need to reconsider who your mates are ;)
Follow how this was designed on my blog https://edditiveblog.wordpress.com/category/beer-bottle-lock/