When somebody gets very cross over something which others may consider insignificant. Also a maddiff is never stated by the other person only observers and people around there. A maddiff can also be online when somebody replies to a comment on facebook etc and gets a bit cross about what was said.
Everyone lAg's (not lag, like I am lagging behind but LahG) at the comment.
Status on facebook: Thanx for the most epic birthday party peeps, I love every single one of you! Best Friends for life :)
Person who replies (close friend): shot for the invite bro'