This hand came up in a teams game at the club some weeks ago. I don't recall the auction, but Jim opened 1♥, I overcalled 2♣, North doubled and Jim ended up in 4♥ (without mentioning diamonds).
I led ♦Q, Jim won, drew trumps, led towards the ♣K (ace played), discarded a diamond on ♣K and claimed eleven tricks, saying "I'll give you a diamond at the end".
I refused the diamond trick, as even though there is a legal play that loses a trick, I thought it very unlikely that he would have lost it had he played it out. I wouldn't have expected a director to award me a trick if it came to a ruling.
Should I have done, and would it make any difference if Jim had omitted the phrase "at the end"?