Quite true, there are probably multiple context specific uses for most of the fandom terms.

What I've seen a lot for 'being so excited/pleased/etc. about something that you can only flail at the keyboard' is "asdfjk" or any variation of that. Some people also just write "keyboard flail".

Another thing I've seen is a huge variety of complicated emoticons to conveying everything from glee to embarrasment to outrage and back again.