You are a woman and you are in this great new relationship with that guy.
Comes a good female friend of yours.
You go for a drink together.
She starts judging that guy, judging what you do, telling you he's not right for you and spreading rumors
If you don't watch out, within an hour you might have totally lost trust in this new relationship.
Your "friend" just painted a picture that was so doomed that you are on the edge of breaking up and finishing it off!
She might just be jealous, resentful because she is single or secretly really like that guy!
Her influence is like a virus!
She is like a toxic substance for your new relationship.
You might start a fight with your boyfriend over it and she might your relationship so hard that it takes you days or week to recover.
In some cases, she might even win and destroy your couple.