How to deal with people and colleagues who are angry, complaining or seeking attention?

For some reason I'm a magnet to bad people or people who are chronic complainers or attention seekers. They often come to me when they need to talk or vent. Especially at work. I don't really want to talk to them but I'm too friendly and not good at setting boundaries and I often just listen to them offering advice. It stresses me, especially when they are angry and they come to me to talk about it. How can I deal with this in a skillful manner? I tried practicing Metta towards them which didn't work due to their negativity being too strong.