OP here. Well, I did say something, in an offhand way, like, "I know this sounds silly but I'm still irritated every time I see my slashed sheet of paper with exercises on it. I couldn't figure out why, until I realized that it's not the piece of paper per se...it's the disrespect displayed when you disregarded my wishes" (or something to that effect). Sure enough, his attitude was, "It's a piece of paper, I can't believe you're making such a big deal out of it." Followed by a list of my transgressions. Sigh. Well I had actually not intended on inviting him in the first place; it was supposed to be just a couple of female friends, but he was doing something for me earlier in the day (as a PP suggested, he does have redeeming qualities) and when he asked what I was up to later, it seemed I should invite him as they were mutual friends.
Interesting to see that not one of the responders here have said, "Oh yeah, you're being silly." And no, I wanted to stay well back while he was playing with his knife. All it takes is for one unexpected move for an accident to happen. I've already been cut once (not by him, about a year ago) when the person holding the knife decided to swing around to put it on the counter just as I was drying dishes and reached out to put something away. My arm collided with the knife and I got a nasty cut. It was an accident (carelessness on the part of the holder of the knife, IMO....you don't make sudden moves with sharp knives when someone is standing nearby) but I now know to stand back when people are holding kitchen knives.