Don't bad-mouth others!
Gossiping can be harmful for you because of a psychological effect called Spontaneous trait transference. When you gossip about others in a negative way, the listeners unconsciously transfer those negative traits to you. As a result, the listeners unconsciously see you as a bad person.
On the flip side, it implies that if you talk positively about others, those positive traits can be transferred to you.
59 Seconds by Richard Wiseman
When you gossip about another person, listeners unconsciously associate you with the characteristics you are describing, ultimately leading to those characteristics being transferred to you. So, say positive and pleasant things about friends and colleagues and you are seen as a nice person. In contrast, constantly bitch about their failings and people will unconsciously apply the negative traits and incompetence to you.
This effect, known as spontaneous trait transference, reveals the pluses and minuses of gossiping.