I've heard the phrase described and used in two VERY different ways.

First: Aspects of the social expectations for men that negatively affect men. (boys don't cry, you must be physically strong or else you are not a man, you must be tall or youre not a man, you must be violent, you must be successful with women, etc)

This one places the blame on societal factors rather than any single person, both men and women are responsible for this perpetuating this one. The "toxic" in the name refers to how the expectation to be masculine is whats toxic.

Second. Common actions committed by men to hurt others (catcalling, rape, violence, sexism, etc).

This one places the blame on men for actions that are committed by other men, and that men are responsible for perpetuating this one. The "toxic" in the name refers to how masculine-attributed actions are toxic to men and women.

These definitions are used by the same groups of people (feminists use both definitions, sometimes interchangeably) most men who find themselves averse to even the mention of the phrase usually defines it as the second.

So here's the question for you, which is the definition? And why do you think defining it as that definition holds significance?