I actually have a good reason to short TSLA (haven't done it myself, mind you): to buy SpaceX
There's
several funds that have SpaceX in them, but only as a small fraction. You could effectively buy a pure SpaceX play by buying the funds and shorting all of the non-SpaceX companies in ratios relative to their fraction of the fund you've bought (assuming they're all public). Said funds often have Tesla in them as well. Hence, shorting Tesla to buy SpaceX
I wouldn't recommend this strategy, however! In addition to it being high maintenance, you'd have to maintain total short positions much larger than your SpaceX position, which - even though they're in effect zero leverage - your broker would require you to tie up significant amounts of cash to do so.