I admit it, it was a mistake to send the party leader "Thanks for the decline" when they opted to actually press the Decline button when Stryde (11 Cler/5 Rang/1 Monk) requested to join a Gianthold Tor group with all classes selected.
The leader replied with "Thank yourself for gimping your toon" (or something similar), to which I simply laughed at. While this wasn't the first time Stryde has been declined (nor the last, I hope), it was the first time someone had actually clicked the button instead of just leaving me in Limbo until the group finally filled.
I was simply trying to let them know that I appreciated the courtesy of the decline, and in my naivety failed to anticipate that they would take it as anything other than a genuine appreciation for their courtesy.
So, if you ever hit the Decline button when a member of the Renderguard guild requests to join your party, please keep this in mind - my reply with "Thanks for the decline " is truly coming from the heart (I added the smiley to show no hard feelings).