When dating, the one thing that is noticeable right away is courtesy. Yes, pulling out chairs, opening doors, and paying the check are all signs of a gentleman (and hopefully that behavior stays throughout the relationship). However, one of the biggest red flags often isn't addressed: How does he treat other people in your presence? Bashing ex-girlfriends, talking trash about friends, snide remarks about your friends... these are all warning signs. And men who need to show their masculinity by insulting/abusing service personnel—food/cocktail servers, coffee shop cashiers, whatever—aren't worth your time. The bottom line: How he treats others is a direct reflection of how he will treat you.