I'm not going to tackle all the nuances of this word. (The podcast 'What A Woche' from the Dinglish-speaking podcaster Gale Tufts did a wunderbar job of elucidatiing the differences between the English 'so' and the German 'so'. (I can't find the specific podcast because it's from a few years back, but listen to her more recent stuff here.)
So, I'm rambling, but what I want to talk about is not 'so' as a pre-announcement, a way of breaking up an awkward silence or broaching a difficult subject, but the kind of "so" that ends a sentence. Or tries to.
It started with the deliberate tailing off of a thought in the hope that the other person will finish the sentence the way you wanted it to end - without you having to say the slightly cheeky or unpleasant thing you need them to know. My temporary boss recently did it when he needed me to schlepp into town myself and hand-deliver my timesheet, as he had already packed up his fax for the impending school relocation and couldnt fax it.
"It's all packed up but they need a copy today, so...". Two letters and three dots effortlessly communicating "You have to spend 2 hours on public transport because it didnt occur to me that I might need my fax machine before the end of term. Merry Christmas!" He left it hanging in the air. Waiting for me to dispel the awkwardness by apparently spontaneously coming up with the genius solution of me going out of my way, which he could then pretend never to have considered.
I played dumb. "So..." I repeated, smiling and nodding encouragingly at him to finish his thought.
"So...well...there's no way WE can get it to the agency for you, and it will have to be tonight so..." Again! I kept the friendly perplexed look up for a few more seconds as he squirmed, and then I played ball. "Well I suppose I can go into town and take it myself after work. I'll struggle to get there before they close though, so..." I smiled at him expectantly again.
"I suppose you'd better leave early, then." Yes! Two can play at that game.
But that's not the worst of it. This spineless get-out clause at least has the quasi-decency to pretend that the perpetrator genuinely hasn't considered the idea that the person s/he is "so..."ing might somehow be able to get them out of this fix by going above and beyond. It's cowardly and passive-aggressive but it in some way colludes with the target audience. What is far ruder is the loss of the ellipsis. The far more abrupt "so."
I first noticed this when a flight attendant pulled this crap on my lactose intolerant partner. She had ordered the VEGAN meal, as 'dairy free' completley foxes them and results in some cheese-drenched polenta creation because someone has their food intolerances mixed up. In this case, vegan had been too alien and they had substituted the vegetarian meal, and as the world of airline cuisine knows, vegetarians subsist on a diet of macaroni cheese. With extra cheese as a vegetable.
"Well we don't have any other meals for you, so." The attendant practically spat when we pointed out the problem. The "so." here meant "Discussion over." She didnt care what the end of the sentence would have been, she had delivered the inedible goop and her work here was done. There was practically a silent "ner-ner-ner" or possibly a subtextual "fuck you". My beloved didn't drop it, though, and I think eventualy scored some sad looking salad from first class. She had to go to another attendant though: as soon as this lady had delivered the final "So.", it was case closed for her.
The only response to this annoying linguistic gambit is to pretend it doesnt exist. To persist in the fiction that the perpetrator really just lost their thread mid sentence, and politely encourage them to continue where they left off. it will confuse - or at least frustrate - the worst offenders, who may not even realise that "so" has never been a sentence closer, but if you're lucky, you'll score an afternoon off, or even a "First Class" (note quotemarks) salad, so...