Here’s today’s halacha: (GTT, pg109)
You may not praise someone excessively in front of a group of people, even though these people have nothing against the subject being praised. Reasong being, a) you may add in something negative, or b) excessive praise encourages the listeners to try and refute you by mentioning his fualts.
Ex: “X is a great teacher, excellent lessons, understands his students, etc…”
This is an invitation for someone to add in “Yeh, but he has a hard time controlling the class sometimes.”