Social media company Pinterest reported excellent first-quarter results, and the stock is now at a 52-week high. My stock portfolio isn't terribly concentrated, and the "largest" stock investment in it has changed a few times over the past couple of years thanks to price movements. Upon logging into my brokerage account about a week ago, I found that it has changed again: Social media company Pinterest (PINS -0.19%) is now the largest stock investment in my portfolio. To be sure, I didn't necessarily plan o ...