A tweet that pretends to show humility but which is actually bragging about something that happened to you. Similar to a humblebrag.
The key to a humbletweet is to pretend you don't understand why you are getting all this attention while also making a blatant attention grab in your tweet.
Examples of a humbletweet:
(sometweeter) > What? Why? "I have one of the top 5% most viewed @LinkedIn profiles for 2012"
(sometweeter2) > Rly dnt dsrv all this #attention 4 ths #volunteer wrk w/the #homeless. Thx!