In your life, you'll meet a lot of people.
There must be a time, when you'll meet these 'toxic people' : people who complaints everything, grunt at things, use sarcasm in every words, will dominate a conversation, all in all, if you are the sensitive type, you'll know they are 'toxic people' when you can feel the negative aura bursting from their body. You don't know why, but you can feel it when they are there and you don't feel comfortable being around them.
You can choose to walk away from them.
Like any other energy, they are transferable.
I call them dementor because they will consume your light.