If I bought 100 shares of Tesla and then decided to sell 1 share for .50 on the market.. once it sold..would I see on the Tesla stock ticker that the price had dropped to .50 at some point during the day??
Yes, but you'd need a lot more than 1 share to do a pump and dump
Practically systems like National Best Bid and Offer (NBBO) stop one-off things like this from happening.
Theoretically, selling a few shares at say 10% of their value would do absolutely nothing to the market because the buyer would just turn around and sell it again at a fair-market price, thus negating your prankster sell price.
If you really want to tank the stock price, you'd need to pull a Pump-and-Dump - it's illegal so maybe not the best prank.