I recently had an opportunity to contact a highly esteemed professional in my field for helping me with a technical post. We met at a conference that we both spoke at. They provided some feedback, to which I responded without proper manners. I didn't show enough respect, and they posted something on their Twitter, essentially saying that manners are very important. I feel horrible, really terrible since I respect and like this person a lot, especially given the free help they gave me.
I want to apologize, but I feel like it would be selfish. I already follow their Twitter, but I don't want it to seem like they can't rant on their Twitter. Right before they posted on Twitter, I had sent them a note with proper manners thanking them for their help, but I feel like one of my emails was very poor form.
How can I phrase the apology? I know that grammar and professionalism are very important. I want to be sure to take 100% of the blame and make no excuses. This is my fault.