Sister in law's 18 year old daughter.
Whole family round at her Grandparents for boxing day, the miserable little sod sits on her own with her coat on for six hours, refuses to eat the meal prepared for her and sulks like a small child.
The rest of 'em are a delight - mother in law is a ringer for Nursey from Blackadder, father in law does a great line in sarcasm and the brother, sister and sons in law are all delightfully odd.
Even the dogs are well behaved
Honestly, why the sour faced little brat doesn't just stay at uni over Christmas is beyond me.