If you go to your System> User Macros screen, and click on a blank space, you can give the macro a name/icon and then in the big space below just type /p then your message, exactly as you would if you were talking in the chat box. That way if you join a party you don't even have to select the right chat channel.
You can either bind it to something or just right-click (Square) select it in the User Macros screen at any time and hit Execute. Saves a lot of time typing out a long explanation.
(Sorry about the very simple level of the instructions, I figure you might know most of this but some lurkers might not!)
I think most people who are jerks or impatient are coming from a position of ignorance. When someone stops moving without warning or doesn't respond to the chat log, they think that they're griefing them and get mad instead of understanding that the person on the other end is suffering from acute pain or some other real life issue at that moment. If was in a party and someone said right away that they had some difficulties but were clearly doing their best, it would really help me understand and be patient. And if anyone else in the party started being a jerk about it, they'd find it was them getting kicked, not the person who asked for some extra understanding.
I said I wasn't disabled earlier but I do have some issues using the standard UI, and one tip I have is that I made Party Chat (and a few other select channels) play a noise when someone types (Character Configuration> Log Window Settings> Notification Sounds). I set my Party channel up to play sound 'Type 16' there, it's not disruptive to me because it's a gentle sound but it alerts me when someone is trying to get my attention so I don't need to keep watching the chat channels visually which makes me a lot less stressed in battle. No idea whether that helps anyone else but it certainly makes things easier for me.