On #12 (which is #3 these days because they are starting on the back), one member of our foursome marked his ball with a tee because he didn't have a ball marker. It was close to my line, and I should have asked him to move it, but I didn't. By my read, I needed to hit my putt just inside his tee. I hit what I thought was a pretty good putt, with a chance of going in the hole, but it hit his tee and stopped dead about 2 feet from the hole. The speed was really good, it would have stopped within a few inches of the cup, and had a chance to go in. But it didn't.
As far as I can tell, no rules were broken here. The rules of golf define a ball-marker as follows:
An artificial object when used to mark the spot of your ball to be lifted, such as a tee, a coin, an object made to be a ball-marker or another small piece of equipment.
I think a tee qualifies. I would have certainly been within my rights to ask him to move it (Rule 15.3-c). But I didn't. So I had to hit my final putt a couple of feet, rather than a tap-in (or possibly even a birdie).
I was putting pretty well today (30 putts). If I had it to do over again, I would have asked him to move it.
On the flip side, if I had hit it way too hard, I would have been glad that it hit his tee and stopped.
Another issue that came up is how do I post my score with a temporary green on #18, and a temporary tee on #1 (taking it from 395 yards to 216). I'm waiting to hear back from our handicap chair on that one.