That he maintains his temper
If a man can’t keep his temper in check in just the first few dates, he almost certainly has anger issues. If you see him lose it on a server who spills something, if you see him aggressively tailgate someone who cuts him off in traffic, and certainly if he loses his temper with you, get out of there. You don’t need to listen to the excuses or reasons he screamed or became aggressive with anybody – whether that was with you, or with someone else in front of you. One standard that’s definitely not too high is simply that dates be able to control their anger. “No rage issues” is a very fair standard.