The TVTropes Trope Finder is where you can come to ask questions like "Do we have this one?" and "What's the trope about...?" Trying to rediscover a long lost show or other medium but need a little help? Head to Media Finder and try your luck there. Want to propose a new trope? You should be over at You Know, That Thing Where.
I think the closest thing there is around here is Explain, Explain... Oh, Crap!
You mean like Alice uses the fact that Bob keeps agreeing to get him to agree to something bad?
Delayed Reaction seems to be at play.
Thanks, Delayed Reaction seems to fit the the most.
Not Listening to Me, Are You? could also work, though it seems to cover the part before the Delayed Reaction.
^ Only in case Alice intended to test Bob with the question.
^ After double-checking the scene (I simply forgot who was "Bob" in that duo, between two possible options), turns out that the phrase to which Alice had a Delayed Reaction was a joke (about them being overly enthusiastic over the topic they're discussing), to which they absent-mindedly agreed.
Bob keeps agreeing to whatever Alice says, and instinctively replies "yes" to the last question as well, only to realise that it was an odd one out. Basically, what's in the title.