It's not that big of a deal, but it's still pretty annoying. I let it go when it's a one-time accident. If the same person keeps doing it, acciental or not, I'll give them a look or say something about paying attention or knocking it off.
15 NS Ripsaw . 14 NS Proto HD . 14 NS Cobra . 13 Gnu Space Case EC2 . 2013 Salomon Pow Snake
14 Now Drive . 13 Now IPO
14 Flow Hylite