A iai doh
Oh, I've doh'ed a lot. What first comes to mind is actually iaido, which we sort of integrate with the aikido at my dojo, so maybe I'm excused?
I was showing the students how to hold the thumb slightly to the side on the tsuba (sword guard), when the sword is sheathed in the scabbard. In case it slips out, you just move your thumb down to the side of the blade, to stop it without cutting yourself. I was very clear about that - thumb to the side, so you don't cut yourself when stopping the blade from sliding out.
Now, although I held my thumb to the side of the tsuba, it was evidently not enough, because when I made my sword slide out and pushed down the thumb, I cut it. There was some generous bleeding, and I had to roll my handkerchief around the thumb.
I looked up at my students. They all had attentive, slightly puzzled faces - expressions that also got me puzzled, until I realized that for several seconds they thought I had meant for this to happen. They thought that was part of the technique.
Well, not for long, they didn't.
Which reminds me of a similar incident - this time an aikido demonstration. I was doing hanmi handachiwaza against yokomenuchi, first just a taisabaki evasive movement - signalling to my uke to make additional attacks.
He did, very quickly, but happened to switch to jodantsuki, and I was probably far too involved in showing my good side prophile to the audience, so he hit me straight in the cheek.
He had a good tsuki. I could both feel it and hear it on impact.
Realizing - with additional surprise - that I was not knocked out, I grabbed his wrist and did shihonage.
Then I looked at the audience. They had attentive faces, not even puzzled. It was obvious that they thought this to be the normal way in aikido to deal with tsuki.
I didn't correct them.