Here's one from a friend this weekend.
She and her FIL do not get on (he is separated from her MIL) and from what she has told me he frequently behaves badly/rudely, yet her DH makes constant allowances for him because "it's hard for him being on his own since the divorce".
(The divorce, BTW, was more than ten years ago.)
Anyway - apparently FIL pitched up at their home on Saturday afternoon, having been invited for a barbecue. He says he has something for them in his car - a new lawnmower, as he knew their existing one was old and past its best.
How kind...until he said: "It cost me £80, so if you could sort that out as soon as possible that would be great. Cash would be best but a cheque is ok if that's easier."
Neither friend nor her DH had not asked FIL to get them a new lawnmower. He did it completely off his own back while he happened to be at the garden centre buying things for himself.
She was gobsmacked - and fuming when her DH got out his chequebook and paid his father back for something they hadn't asked for or planned to buy in the first place.
I feel she would have been within her rights to say something along the lines of: "FIL, thanks for the kind thought and you're right, our lawnmower is starting to wear out. But we weren't planning on replacing it just yet and hadn't budgeted for a new one. We really appreciate the gesture but would ask you to return the new lawnmower to the store and get your money back."
Sadly, her DH's compliance in paying up meant she didn't have the opportunity to refuse the "gift".