Obviously in this case the thumping worked for some and turned other people off. I don't think it is disrespectful or negative to discuss this on a music forum. If I were the performer, I might want to be made aware that some people thought my foot tapping was too intrusive, and I could then decide whether or not to modify it or leave it as it is. Feedback, positive or negative, is valuable. I would hope this thread wouldn't put anyone off from going to see this duo - they are certainly worth seeing. Go to their next gig near you and judge for yourself.