uso_desu
This tag referes to the ASCII-art "uso desu" (ウソです) which means "it's a lie,"and is used in 2channel, Japanese biggest BBS.
The AA is as following
* *
＊ ウソです ＋
n ∧＿∧ n
＋ (ﾖ（* ´∀｀）E)
Y Y ＊
and used to completely deny all text written in the 1st comment of the boring thread (mainly in 2nd comment.) Additionally, it is a kind of manner in 2ch to write "A lie, I see" (なんだうそか) immediately if you see this AA.
Usage Example (2ch style in English)
Thread title : I found pretty innovative fact !!!!
1 Name：VIP warrior [sage] date：2008/12/07(Sun) 14:15:52.88
Chocolate dissolves a chewing gum in your mouth!!!LOLOL
2 Name：VIP warrior [sage] date：2008/12/07(Sun) 14:17:39.12
* *
＊ ウソです ＋
n ∧＿∧ n
＋ (ﾖ（* ´∀｀）E)
Y Y ＊
3 Name：VIP warrior [sage] date：2008/12/07(Sun) 14:18:16.39
A lie, I see.
Unrelated to uso da.