Pretty obvious - no-one likes Blackpool FC.

Actually Santa clearly states what the significance of "tangerines" are early on in the script:
"They're my signature gift" he states "that and the walnut".

Satsuma is more fun to say.

Isn't Clara from Blackpool ??

In reality how many kids nowadays get tangerines.

Back when the tradition started it was because fruit like that was a rare luxury but now you can go out and buy them everyday if you wished

Exactly. What was rare is now an everyday occurrence.
They were never really liked for what they were anyway.
They just signified the season, a symbol more than anything else, more of value in their symbolism than reality.....and symbols can be explosive.

By Jove, I think you've cracked it.

Santa's really saying 'no-one likes Clara'. Moffat's hidden message.

As I said earlier they where not important and people where reading to much into the tangerines!

Well I saw it as a throwback to the first Xmas episode with the Sycorax. After the fight he pulled one of his pocket

Yup, that'll be it. Mystery of the tangerines is solved.

Sherlock, schmerlock. Meh.