Aren't Avatar by nature usually small? I would consider most Avatars to be "thumbnail" sized, but yes, they would be maybe 50 x 50 pixels.
Well, I was asking about your own Username. (You know what you look like, right?) :lol:
Here is my thinking...
Having a Thumbnail Picture/Avatar allows the viewer of a PM to quickly identify who the Sender/Recipients of the PM are.
If you are the Sender, then you want a visual queue to help you see TO WHO you sent the PM.
If you are the Recipient, then you want a visual queue to help you see FROM WHO is the PM coming, as well as TO WHOM ELSE the PM was being sent.
(In either case, you know what you look like, and seeing a Thumbnail of yourself is just one more thing you have to "filter out" from the listing of Thumbnails. So, to be blunt, your own Thumbnail is extraneous!)
Following that line of thinking, here are a few options...
1.) Include Thumbnails for every party to the PM. (Easiest to code, and non-discriminatory!)
2.) For yourself, instead of your Thumbnail, use a Generic Thumbnail (e.g. Post #3). This helps offset YOU from everyone else.
3.) For yourself, just show a Text Username (with maybe a White Blank Thumbnail to help with spacing). This also helps offset YOU from everyone else.
Or maybe there is another option that is better? :-/
Follow my thinking?