Slightly off the topic but my elderly mum has a neighbour, naice family, 3 DC, naval officer DH, all OK, who moved in, oh, 12 years ago (Mum's been there 40 years). They put up one of those stand alone double carports in their front garden, brick built, raked tiled roof. The back of it is actually on the boundary line and the gutter overhangs mum's property by the 3" that gutters do. Whilst building this, neighbour asked mum if it'd be OK if her builders put up scaffolding in mum's front garden etc which mum agreed to 'as long as they made no permanent mess' which they didn't. She also had the builder's vans parked on her grass verge (only chipping them for chucking cementy water in her drain- rural, I should add, all gardens 1/4 of an acre- for weeks (other works going on inside the house).
Anyway, the dividing fence is 6' wooden panels, mum's responsibility. The panels that ran between mum's shed and the windowless side of her house were collapsing, so, 4 or 5 years ago, after informing the neighbour (as they have a dog) DH and DB set to and did the replacement properly, taking out the rotten wooden posts and replacing them with cemented in posts that you slide the wooden panels down into. Hell of a job, but the end the result was smart and semi-permanent.
All OK. Til a couple of weeks later, Mrs neighbour arrives on mum's doorstep, still all polite and pleasant, just wanting to 'inform' mum that one of the new fence posts encroached on their land by 'an inch or 2'. 'If you stand on a box and run your eye along the line of the fence, it deviated towards our property a bit at that point..... Just so you know'.
'Oh, OK' says mum.
End of story.
I was ready to serve them a notice to take their bloody garage roof guttering down but find another solution for their nuisance rainwater run off etc etc 
I just think they didn't stop for a moment and go 'Hang on, we get on perfectly well with the elderly lady next door, she chucks our kids balls back without complaint, she never complains about high jinx in our backyard, she takes in parcels, she let our workmen erect scaffolding in her garden for weeks to build our garage, let's just let what was obviously a slight error, even of 'post-crete' concrete drying, go, shall we?'
Luckily, nothing more was said or done but it still irritates me that Mrs Neighbour was prepared to jeopardise the good neighbourliness between them over that.