|November 17th, 2014|
|gender, ling, they [html]|
- Jeff lost their hat.
- When you see Jeff, can you give them this note?
- Jeff's borrowing a car, so they can drive themself there.
These are currently confusing to most people, so you probably want to think about context and not use them when it's not worth it. Still, the more we hear "they" the better it will sound. For example, two years ago uses of "they" like "whenever I meet a cute boy contra dancing I friend them on facebook" sounded wrong to me, but now those sound fine.
(And if your response is "but 'they' is plural, you can't use it in the singular!" then I would say "using 'you' in the singular was once just as wrong.")