If you are going to comment then it is better to do it in a 'friendly' way (as hard as that can be!!), giving some links to the RWAF Rabbit Welfare leaflets. If you post a long rant then the person will just delete you and ignore you. That wont help the Rabbit.
I do know how hard it can be not to go off on one when you see a Rabbit kept in dreadful conditions. But from past experience I have learned that the louder you shout the less people tend to listen
You can always punch a cushion and pretend it is the person and then be sickly sweet to them when you post your advice !!