"Threats to your masculinity" the feministy-toxic way of saying: I feel insecure of how others will react if I don't behave like I believe they expect me to.

As for "reactions to a threat on my masculinity" you'd have:

• Reaffirmation: Like picking fights or extreme bravado. This is usually due to some kind of previous emotional/physical abuse or living in a harsh/over-competitive/over-bearing environment. You harm someone due to the fear/habit of being harmed first. Think of it as a mild sort of PTSD.
• Conformity: This is fear of rejection. You see it a lot in boys, especially those who have shallow relationships, few friends, or receive little love at home. Boys love is a fickle balance of teasing and affection, so if they tease you with being girly and you somehow feel afraid that they might dump you, then it's safest to stick to the pre-conceived social norms. Later in life men make habits out of this dynamic.
• Hatred: When people fail to adapt to change, the feeling of instability causes fear, which then triggers hate. It's fear of the new and unknown. That's why you see this more prominently displayed (though not exclusively) on the conservative, religious, and elder.

So, as you see "what do you find are the greatest threats to your masculinity" is kind of a trick question because masculinity has less to do with conduct/preferences/beliefs and more with how you respond (or react) to the pressures of the environment.

Nothing can threat my masculinity because male is part of who I am. It's how we shape and define it as a society that can became a threat to others and myself.