IMO the best way to spot a jerk is how they react to their own screwups. Everyone has been there at some point in their career, whether it's rm -rf / on a prod

IMO the best way to spot a jerk is how they react to their own screwups. Everyone has been there at some point in their career, whether it's rm -rf / on a production server, or forgetting a WHERE clause in a DELETE query - you WILL fuck something up, and it'll be something important. Now, a normal person will own up to their mistake, use it as a learning experience, laugh about it, and maybe ask someone for help. Take the mickey a bit, but don't give them too hard a time. They know what they did and they respect you, which is why they asked you. This leads to the second way to spot them: do they take other people's advice or suggestions on board? Even if they don't think it's the right solution, do they engage politely in a constructive discussion? Nobody is an expert on everything. If they don't do either of those, you've got a narcissist on your hands. Another thing to bear in mind is that occasionally a particularly egregious asshole needs taking down a few pegs. That's how you handle bullies - you take their perceived power away.