What the fuck does MRM mean?

MRM refers to the myreadingmanga.info website, which manga are more about smut and porn. Not really a good option if you're looking for a good plot, but perfect if you just want some smut. The problem being that you will find many manga with rape, pedopornagraphy, etc. in MRM, so people on mangago will often complain whenever a manga "escapes" MRM and find its way on mangago.
I hope my answer helped you.

Thank you very much! You gave a great explanation and helped me understand what this mrm means. Again, thank you!

LOL as if mangago isn't packed full of rape porn yaoi that everyone here just ignores as long as they end up in love in the last chapter -.-

Wooow!! Thats so truth! If they like the final chapter or the rapist is now "sweet" they forgive everyting

Ok, so, just to be clear: check my answer again, you will see that I never said mangago was clean either. Because, yeah, mangago actually has its fair share of yaoi plot-based with rape, I certainly will not deny it. And yeah, though you didn't explicitely wrote it, I agree with you, it can be quite annoying how the community actually forgive anything as long as it's romanticized.

It's just that (in my opinion) MRM is worse in this regard, with many work without any real plot. What's more, mangago is not just about yaoi, you will find many genres (fantasy, action, shojo, shonen, etc.) that you will not find on MRM, because MRM is a website who specializes on smut (again, that's mostly my opinion, I'm not sure if it actually specializes on smut, but as far as I know, it's true that you will not find fantasy or action manga).

I would add that MRM is no longer accessible in France, the government has taken action to close the access in the country. So, I guess some people are actually worried the access of mangago too will be closed, not because the scans are illegal, but because of all the problematic content of some mangas who leaked from MRM to mangago.

English isn't my native language, so, I hope my answer was clear.