In a noisey cockpit, for example, "Yeah, I'll try that too." could be misheard as "Yeah, I'll take flaps two." If the PNF responds with "Speed checked, Flaps two", there needs to be time for the PF to shout "NEGATIVE!" before the selection is made. Flap calls, of course, are not the only ones that can be misinterpreted - as in "Cheer-up!"
Below 10k feet adherence to sterile cockpit (avoiding unnecessary chatting, like the
underlined above), will avoid that. Especially if hard at hearing I would advice that...
Besides, even if we did chat about which mood we are in (cheer up buddy), it doesn't change what I wrote in my previous post. Everyone is equipped with a brain and the ability to think for themselves.
If misinterpreting chatter for flaps 2, while being outside flaps 2 operational limits and then selecting flaps 2, the person in question shouldn't have been in the cockpit in the first place. More appropriate would be to use the brain and make you colleague aware that you are outside flaps 2 limits - which would then clear up the confusion (that shouldn't have been there in the first place, had sterile cockpit been adhered to). If indeed inside operational limits for flaps 2, and it is selected prior to what the PF had desired, tough luck... the he will learn only to make standard call outs during critical phases of flight.