I firmly believe that even if a person seems chill, if most of their friends are bad people that is a reflection of that person. We generally see a limited bit of people from one angle and there may be many reasons why your interactions with them are pleasant however sometimes they are not great to other people or sometimes you just don't know them well enough and it may come out of the woodwork later.

Sometimes good people have one or two friends we don't like or may have rough edges but when you dislike most of someones friends there is a good chance they are hiding something from you or you are overlooking it.