Painted a bright red stripe on all my personal tongs. This simple mark made it clear which tools were off limits for casual borrowing. We then set a firm rule that any borrowed tool must be asked for and returned in the same condition. It stopped the mystery bends and kept things fair.
What's the worst tool damage from lending gone wrong? I borrowed a buddy's vise and cranked it so hard the screw stripped, totally my fault. That mess taught me to mark my tools with ugly spray paint. A clear rule stops the guesswork and the guilt. Just ask first and return it clean, it's that simple. My bench is a no-touch zone now, saves my tools and my temper.
Marking tools with ugly paint is a solid plan. My personal favorite is watching someone try to use a spray painted wrench, then realizing it's not theirs and putting it back. The guilt trip works better than any lock. A stripped vise screw is a tough lesson, but at least it was your buddy's and not some random guy's. That kind of damage can turn a friendship into a business transaction real quick.