Grandfather taught me that if you're not sure what to say, try "Thank you."
"Here's that report you asked for."
"Thank you."
"Have a good time!"
"Thank you!"
"I'd like to offer you some feedback."
"Thank you."
"F*** off!"
"Thank you."
You could say nothing. You could smile, frown, or stare confrontationally. You could say, "Okay", "I will", "On what?", or "F*** you, too!"
Those other approaches could minimize something nice or escalate something violent. Saying thank you is positive, genuine, and de-escalatory.
Who can argue with being thanked?
Grandfather was astute politically. As a leader in higher education, he continually faced the brutal* politics of academia. He was described as an "emergency medical technician" who would come in after university leadership had lost everyone's trust, mop up the blood, lower faculty blood pressure, and set the next leader up for success.
He grew up in rural Louisiana and married a city girl from Baton Rouge. He worked the radio during WWII, then went north for his education in public policy. He lost his accent but always felt more comfortable in a sports coat, especially for dinner. He made a career out of building institutions (governmental and academic) that worked for everyone. One key to that was easing tensions and fomenting trust.
He taught me a lot. The value of persistence. The value of honesty and integrity. The importance of public service, of taking care of everyone. Poise. Curiosity and keeping up with technology. He read to me, and taught me to e-nun-ci-ate.
He taught me grace. And to be thankful.
* Why are academic politics so brutal? Because the stakes are so low.