Don't know why i'm thinking of this now but has been bugging me... I obviously have too much time on my hands! 
A friend of mine has a birthday that is 4 days after mine (at beginning of Dec), and we have always sent each other birthday cards. FWIW I always pride myself in sending friends cards and remembering birthdays, even if I don't always get one back. I received her lovely card a few days before my birthday and thanked her for it on my birthday. Then there was the heavy snow, and so I ended up posting her card a couple of days later than usual (was/am heavily preggers so wasn't very safe trotting up the road to buy and post card at the time). I text her happy birthday on her special day, and warned her that her card would be a bit late because I had posted late and because of Royal Mail having probs with the snow.
All seemed fine, but turns out she never received my card, as 3 weeks ago, she posted on my Facebook wall for all to see:
"Still no birthday card. Oh well, maybe I'll get it this time next year, haha. So how are you?"
I think I was pissed off because a.) I always remember her birthday and it made me look uncaring b.) She's had previous of doing this sort of thing before but in front of other people i.e. put me down but then say "i'm only joking, haha". 
AIBU in thinking that this is a very passive-aggressive post? or am I over-thinking things? I'm not generally a sensitive soul but I was miffed because she had text me earlier that day and so could've said the same thing in the text if she really wanted to, and also she hardly ever fbs me any other time.