It's when a man is forced to act a certain way because it's what men are supposed to do regardless of what the person thinks. or believes. Example: Men are not supposed to like pink because it's too girly. So a men should not mention that they like pink even when they do. Another more serious example is that men can only express one emotion and that's anger. Men can't show joy, sadness, or any emotions that show vulnerabilities. This causes a substantial amount of men to suppress their emotions and that could be very negative to the mental health of these men. That's toxic masculinity. It also can extend to insecurities regarding gender roles and it has broad implications.