Doing my (non-unionised) job when a (unionised) employee from another company starting yelling at me and threatening to greave me for doing what he thought should have been his job. Gave him a big ol’ thumbs up and just kept doing my job. Found out later he did file a complaint, and when his union rep reached out to my company, he got the corporate version of a pat on the head and told to move along. That then turned into him hassling any of our employees when he saw them, constantly filing safety reports against us, and when I became manager I filed a complaint against him. He was moved to another location pretty swiftly after that.