gamma ray burst is a fun one (though unlikely thankfully!) -- a similar one that gets me excited is "false vacuum collapse" whereby the "energy" of the fabric of space itself is at a local but not global minimum. So in some unspecified conditions it drops to a lower/lowest minima and a destructive wavefront expands through the universe at the speed of light. Since the universe is so large, maybe one is already expanding right now, you'd never know (since speed of light). The upside is you'd never know it happened since death would take nanoseconds. Last I read about it, we don't know whether it's a local minima "false vacuum" versus global minimum.