One of the worst is socializing women (and other men) to respond to male vulnerability with disgust.
It's not always contextualized as "men don't cry," either; I often see that knee-jerk disgust phrased in entirely misapplied progressive language, from people who know better but (like most of us) struggle to escape the biases of their culture.
Either way, men crying is always portrayed as a pathetic joke. Men expressing fear, uncertainty, or sadness, gives "the ick," or makes you "gay" or "a bitch" depending on the audience. Few benefit from this: not the individual man, who increasingly hardens himself to avoid humiliation, and learns to turn every emotion into rage. Not women, certainly, who are often victims of that rage, or must struggle with a partner that is emotionally stunted. The only people who benefit from this are maniacs like Andrew Tate, who see mistreated men as a revenue source, and right-wing pundits and politicians, who know one way to keep their stranglehold on power is to whisper to the working man, "Hard men create good times."