If you are trying to complete this week's challenge - The Hell's Kitchen, you may have noticed that one of the objectives is to insult your coworkers. That said, Insulting your colleagues is very easy and can even be done to other people in the game.
However, doing so will lower the relationship meter to whatever person you use the action on, and in rare cases, can result in death. These cases are most likely only for mafia members as if you annoy a Godfather - they might wack you.
Nonetheless, you can insult anyone in the game by clicking on their profile under relationships and clicking the action that says insult. Using this action will then have your character in the game proceed to insult the character you selected to insult.
This will, in turn, lower the relationship bar and, in some cases, cause that person to become your enemy - if this is your goal, you may need to use insult more than once or do other hostile actions such as start a rumor for it to work.
In the end, repeat the process with 21 colleagues to complete the fourth quest in The Hell's Kitchen challenge.