Wiktionary
protest too much
vb. (context idiomatic English) To insist so passionately about something not being true that people suspect the opposite of what one is saying.
Usage examples of "protest too much".
The Swiss are very good at looking the wrong way when it suits them: but for reasons of our own we find it convenient not to protest too much.
I mumbled that I was not in any need of her at the moment, but I could not protest too much, with six or seven of my comrades standing about and grinning at my discomfiture.
Methinks the Vulcan doth protest too much, the commander reflected.