I have one of these cups, and I'm pretty sure most of you do, too. Be careful with those Yeti cups and make sure you're not just throwing them in the dishwasher and expecting them to get clean!
Turns out, bacteria can form under that little rubber seal, and that bacteria can be EXTREMELY harmful and even fatal if it gets in your system. So make sure you're hand-washing under that seal before you toss it in the dishwasher, so nothing like this happens to you.