Caught Masturbating?

How many times have your parents caught you masturbating? My mother has walked in on me twice... :(

I don't have a lock on my door and yet I've still never been caught.  I can usually tell when my Mom's gonna come here when I hear her footsteps, so a quick ALT+F4 + me pulling my pants back up and all she sees is me staring at my desktop for no reason.