I think my biggest one was when I livestreamed me going to the mun for a friend. My ship was built nicely, had a return stage too (I usually leave them there as monuments ^^'). As I was nearing the mun I went to hit M to see how far off I was...I hit space, I panicked and hit it again, separating my lander from my last booster stage...which still had thrust. It ended up hitting my lander just right to knock the capsule of but leave everything else as it was. Needless to say, the Kerbals on board got onto the mun, albeit at 300m/s.