Toxic masculinity is a psychological concept where long-established social norms from generations of use are causing harm to others in society and to the men themselves. Some of these harmful ideas include things associated with being an "alpha male", who dominates others around them, denigrates and demeans women, acts homo- and transphobic, and hiding emotions.
These ideas have been around for ages. I was reading a lot of short horror fiction written by women for an MFA class. Back in the 1800's, even the women were writing patriarchical stories where the men were the strong, silent types who took care of things whilst the womenfolk swooned on the settee. Men didn't cry unless they were effeminate, and some outright equated emotional men to women -- and it was meant as an insult to the men.