I have green coraline growing on the edges of my tank glass where the mag float can't go without causing a sand storm and it grinds my gears when people look at it and tell me I've missed a spot.

Honorable mention- when I have maastards over to pickup stuff and my snails/hermits decide to crawl on EVERY frag I want to show off and they close up only to open when my visitor walks out the door.