DM behavior improvements
If you write a DM but have no users specified it should warn you that there are no recipients
If you write a DM and mention multiple users it should warn you somehow. e.g. "@hj hey buddy, @shp is being a real jerk to me I wish he understood I don't think he's really a Swedish Fish" <--- this sends the DM to both @hj and @shp which is ridiculous from a UX perspective; there has to be a better way to deal with this so users aren't accidentally DMing other users they want to mention by username.
I would even be OK if a DM required a special "To: " field to appear like a Subject so you can put the recipient specifically in that box. Although I suspect this can't possibly work without backend API changes.