This may sound horribly ungrateful of me, but I wish K wouldn't upgrade my drink to a large every time I drop by the shop. It always ends up tasting really diluted, and I happen to be unusually particular about the level of sugar in my milk tea.  To decline his nice gesture would be rude; however, to make requests would be inappropriate. 

E finds this all very entertaining--"Such a dilemma," he says.  It boggles his mind how I'm trying to avoid this benefit I'm being given due to quirky personal standards.  According to him, the fact that it's free should compensate any negative factors involved.    

So here's the win-win solution R came up with:  From now on, I'll order her drink, in which he'll will upgrade to a large, and she'll order my drink, which will stay the same size because he's not familiar with her.

(I must say, she happens to be quite brilliant when her own self interest is involved.) 

Sorted!  This plan shall be implemented starting next week.