It’s a phrase that sort of kills the conversation. Grumbling may be the thing that I do best. There’s something very British about it, as we seem to have specialised in grumbling on a scale that is unheard of.
There are of course legitimate reasons to grumble, loads of them , so plenty of fuel for the fire. But the grumblers seem to have the upper hand in almost everything, and some earn a living from it. I find it difficult to think of the opposite to a Grumbler, perhaps we can find a word for those people who are irredeemably cheerful and positive. “posidrivers? “ Nope, sounds like a cheap tool set.
I’m sure you might know someone who is like this. I recall a young chap I did some work for when working for the print company in Gloucester. Effusive, energetic, positive and ambitious, he said he wanted us to print a business card for him that would be the best we’d ever printed! And we did. He once came into our open plan sales office, peopled by people slightly less enthusiastic than himself and smilingly told us all evangelically to “Keep on doing what you are doing” to a sort of bemused silence. Lovely bloke considered by the rest of us a slightly strange. Positivity was not the watchword in the place. None of us there forgot it, and the phrase was adopted by one of us as a sort of gentle put down, especially when someone had cocked up a job.
Have a grumble free day!

How could anyone possibly grumble at that wonderful view of the British countryside.
Thanks
John