What's going on with the "Make Mine Milkshake" thing I keep seeing on Twitter, and what does it have to do with comics and feminism?

As best I can tell, it started with this account, maybe posting a selfie or something? But suddenly every comic book fan, writer, artist, etc. that I follow is posting this with #makeminemilkshake and making references to supporting feminism. What's up?

Examples:

Example one

Example two