A quote from Camille Paglia (a self-proclaimed feminist)- “When an educated culture routinely denigrates masculinity and manhood, then women will be perpetually stuck with boys, who have no incentive to mature or to honor their commitments.”
I have read articles that suggest using phrases like “Man Up,” or “Be A Man” are harmful and abusive to boys. Which I personally think is a sack full of rubbish.
As a society, we want our boys to progress along the lines of maturity, and transition from boyhood to manhood. I have used and continue to use both of the above terms in my vocabulary. I have used them raising my son and I have used them in my man-to-man relationships. I have also used the ever popular, “Put On Your Big Boy Pants.”
A quick Google search (see attached photo) revealed the most popular synonyms for the phrase “Man Up.” As you can see, this is not a list of disparaging descriptions. To be a man and act like a man means to take responsibility for yourself and your actions. It means, to stop acting like an immature, snot nosed, self-centered, undisciplined, pampered, crying to get my way, boy.
In the masculine vocabulary, the terms “Man Up” and “Be A Man” are terms of affection and love. As a society we have a responsibility to instill in our young boys the virtue of manhood. Not to disparage it.
All of that to say, toxic is not a synonym for masculinity. Some of the best encouragement and advice a young boy or grown man can receive from someone is to be told to, “Man Up” or “Be A Man.”
If that offends your sensibilities, a more politically correct and more inclusive phrase comes to mind. Suck it up buttercup. 
Manhood is the ideal that all boys should aspire to.