The following sentence
I didn't meet you today so I could drink coffee.
could be parsed two ways:
I met you today, but the reason was not so I could drink coffee. (It was so I could discuss our divorce.)
and
I did not meet you today, and the reason was so I could drink coffee. (Starbucks had a half-off sale on cappuccinos today.)
The first way is widely used, and I think it can be confusing, as the sentence contains the phrase "I didn't meet you", while the intention of the sentence is to say "I did meet you".
Which is why I always try to say:
I met you today not so I could drink coffee.
Or the common alternative:
I didn't meet you today just so I could drink coffee.
Is there a name for this construct?