What was your first RV noob disaster (or near disaster)?

I had only parked my TT a couple times, and only on level ground.

I was parking at a National Forrest campground and I hadn't set any chocks or anything when I popped the hitch. The trailer started rolling backwards.

I foolishly tried grabbing it. Not a chance.

Lucky, they had installed a 'dead man' for fools like me; a concrete bar that stopped my rolling with a bang. If that hadn't been there, the trailer would have gone for a downhill roll into other campsites.

At least I never forgot again.