Thing To Do Today But Only In A Good Way: ferment.

It's usually yeasts that ferment - that is, change sugar into ethyl alcohol: 


(Photo by Cjp24. That's red wine in those tanks.) 

but it is possible for people.

A person who's fermenting is stirring up trouble, or seething with excitement.

It can make a nice change in a dull and disillusioned world:


(Photo: wikimedia commons and Ralf Lotys)

 or, on the other hand, it can be hugely destructive:

 



On reflection, I suppose it might be sensible to proceed with caution on this one.

Thing To Do Today But Only In A Good Way: ferment. This word comes from the Latin fermentum, yeast, from fervēre, to seethe.

NB Foment is a similar word and it can mean a similar thing - to stir up trouble - but if you use foment then you have to be fomenting something. You can be left fermenting; you can't be left fomenting*.

*When I say can't, what I actually mean is that a few fussy people will raise an eyebrow in happy contempt if you do. 

But, hey, they probably don't get that much pleasure out of life...