It’s no secret that dudes are creeps. Then the internet came around and made it a whole lot easier for dudes to be creeps but in the form of a reply guy. It’s such a common term now that even dictionary.com has a definition for it:
A reply guy is a term for a man who frequently comments on tweets or other social media posts in an annoying, condescending, forward, or otherwise unsolicited manner–especially posts by women. It can also refer to a person who frequently and zealously responds to posts from famous people on Twitter.
That’s a pretty thorough description but you could also just look at these reply guys making everyone uncomfortable on Twitter.