Years ago I had a MM playfield glass explode while I was holding it (unfortunately most of the glass went in the machine).
Most recently, I was setting a Demo Man translite glass down when it exploded. It had the plastic edges and everything on it, and I don't think I hit anything, but it made a mess on the floor. Luckily it was about $15 for a new glass. But yeah, it sucks when this happens. At least it wasn't an actual backglass. Stuff like this usually always happens 5 minutes before a sale or party.