Canned fish with the ring pull. Even if you don't bend the heck out of the can pulling it open, the top always snaps into a funny shape when you get it off, splattering everything within 300 yards with kippered herring juice. Ditto on the molded plastic packages. Tinsnips work pretty well, but butane soldering tools are the best.
Oh, and whoever makes transformers. It seems like they were designing bombs, and just built in the electrical capabilities as a secondary function.