You seriously have to be careful what you say to a tower controller. They are 'agents' of the FAA and anything that you say can and WILL be held against you. The big trick here is that they don't have to tell you that. If you say, "yes sir mister controller, I'm really sorry about taxiing across that runway, it'll never happen again", you may think that everything's a-ok because the controller was understanding and really nice, but really you may have just sealed your fate.
I'm just completing an introductory aviation law class that even goes as far as to say that you shouldn't call the tower. And if you're asked to visit, don't show up. Call your lawyer. She described one case that she almost won. Apparently, the pilot was asked to visit the tower, which he did. At the hearing, she had her client stay at home. When she cross-examined the tower controller she said, "Do you see the pilot here today?" After putting his glasses on and looking around the room, he could not identify the pilot. Unfortunately for the pilot, he signed the guest book at the tower. He lost.
I don't know if I'd have the balls to disobey the tower, but the truth is, once you're on the ground they have no authority over you.
Same goes for FAA ramp checks. Don't start talking to somebody about that time that you buzzed the beach over at Daytona. You may just be talking to somebody from the FAA. They don't have to identify themselves unless you ask. And for part 91, you don't have to let them in your airplane if you don't want to. They can look through the windows, but that's as far as they can go.
Obviously this can all be avoided by being as safe as possible, but we all know that mistakes are made. I've made several myself. Just remember though, if you make a doozy, report it to NASA and that might help you to get out of a pickle.