If someone was spraying acid with a hose, you wouldn't stand there and take it or even take the hose from them to spray others. You would, hopefully, find the source and turn off the hose.
The same goes for negativity. If someone is negative to you, don't receive it and please, whatever you do, DO NOT SPREAD IT.
Your mindset is your property and responsibility to manage. No one else can do it for you.
Paul Goldsmith shares a few thoughts on how he thinks about taking ownership of his mindset, coaching others, and takeaways from the book EXTREME OWNERSHIP.