Quick Definition: A unconscious process of a person to associate the bringer of bad news as “bad” or “unfortunate” themselves.
In medieval days, kings would have messengers beheaded if they communicated bad news inappropriately. Generally speaking, you want to always to be bearer of good news, or, communicate bad news in a more friendly, less severe way. Because the emotion experienced is usually very strong, the person receiving the news is usually associating those emotions with that person. This is why no one likes to say tell a friend that someone is cheating on them.
Sometimes, guilty by association also means that if a PUA member is acting in bad faith at a venue, others can assume that because you are friends with him, you share the blame. Extreme examples of this include overly negging or insulting a girl. Sometimes, the person can be kicked out of the club with his friend too.
The company you keep is a strong reflection of who you are and what you stand for in life, so, choose them wisely, for it is far better to be “fun by association” or “innocent by association” rather than “guilty by association”.
His behavior was so rude that it was inevitable that we got rejected because we were guilty by association.