Tricking your sub into getting something else.

[Rhabbi]

And back on the original question's content- I don't think your "trickery" of surprising the sub with urine instead of semen is a bad thing- I would not even term it as a "trick". However, your lying about their displeasing you is the bad part. In fact, that shows a great lack of true mastery ability.

I'm sure every true sub, slave, Dom/me, Master, Mistress knows how powerful the thought of displeasing the one you serve is. To use that deceitfully is terribly immature, unfair, irresponsible, unproductive, and destructive. Just the opposite of what a good D/s relationship should be.

I think you just summed up the problem here Eponine, very insightful.