Just met a group of "fun raiders" in Master Builders. Really got upset.

Along with using /report, a more effective way to report players would be to join the StaffRequest community. You can use the community chat to to globally contact staff members and if someone is available, they will come help you with any issue that you are having. Otherwise, you'd have to friend staff members in-game and just check your friends list for someone or check out Lobby-1 to see if anyone is online there. I know it can be hard sometimes to find someone, but hopefully, this helps a little bit. Also, keep in mind that you can /ignore any players that you don't want to see their messages. If someone is being rude to you, I would suggest gathering evidence to report and then ignoring them.

 

There USED to be an in-game report for Master Builders.. but they removed it and unbanned everyone from Master Builders who was banned in Master Builders for reasons like this.
So, basically, no. There is no easy way to report them anymore unless you use Staff Request and there happens to be a staff member who is not currently occupied with another task.
To be completely honest, this is the exact reason why I completely stopped playing Master Builders. Nearly every round, there's a group of 5-6 people who build male body parts, discriminatory illustrations, and who purposely say racist, uncalled for, offensive, vulgar and purposely aggravating and triggering negative phrases for the sole purpose of making people feel like worthless, powerless, and defenseless, as well as to make them feel offended and personally attacked.
9/10 times, whenever I experience this, there are usually absolutely no staff members available to deal with this, and my /reports get marked as expired. I would report them on the forums; however, these people make use of alternate accounts that they purchased in bulk for little more than 2 dollars, making any report towards them a complete waste of time and deeming any action against them as completely and utterly pointless.