My worst experience was with my current PC build. I would be in the middle of a gaming session or a just even browsing the web, then the screen would go black and I would be stuck in a boot loop. The only way to get out of that boot loop was to reset the CMOS of my motherboard.
After a lot of troubleshooting I realized that my issues was mainly related to one of the 8 GB stick of the Corsair Vengeance Pro.
Needless to say, those were some pretty frustrating couple of days