In case others haven't noticed this one, it is mentioned in an automated response after reporting RMT's.

If you know of/thought about this macro yourself then props to you, and you can continue on with your day however if you haven't:

/blacklist add <r>

It will obviously blacklist the last person that sent you a /tell (a confirmation box will show) but it definitely beats opening up your menu or typing it out manually... Shove it on a shared bar and just click it when an RMT sends you a tell.