reminds me of a neighbour we had many many years ago when i was still just a small child (in kindergarten). don't know what is wrong with him - he has the corner unit and our flat was just next to him. my mom kept some pots of plants outside our home but it's not situated in or near his 'compound' at all. he would complain that the leaves dried up and fell on the floor, wind then will blow until his doorstep so my mom stopped keeping plants. btw my mom wasn't the only one on the floor keeping plants - he had some too!
one day, she bought me a nice pair of white sandals. we left it on our doorstep. next morning, it was missing .. my mom went to search for it and found it thrown onto the parapet. the last straw was when my mom opened the common rubbish chute and smelt kerosene in it - she was so frightened that he would set the house ablaze (that time my dad was working night shifts which leave my mom and the kids only at home) so we moved out. the person who subsequently moved in didn't have good relations with him either .. don't know what was his problem.
his family members were all nice, except for him. his son even went to our flat to apologise before we shifted out, saying he himself doesn't understand his father's behaviour.
thankfully we've had good neighbours since then - the current neighbour staying next door to my parents sell carrot cake and on some days, he would pack some to give to us for dinner .. when he goes away for vacation, he'd ask my mom to help water his plants.
and so far, since i've moved out of the family home, i've also encountered good neighbours .. i used to stay in a walk-up and one of the upstairs neighbours will walk their dogs in the evening. she and her husband would tell us to go into the apartment first and then they'll come down with the dogs .. there is a family with young children on the ground floor and the kids love to say bye-bye to us when we're leaving to go to work ..
once our drain pipes in the toilet choked, causing water to rise and we were worried it might leak onto the parquet flooring if we left it until morning so we called a plumber at 2am - he checked our place first and then said he needed to check the neighbour's toilet downstairs too .. we were in a dilemma cos it was very late and didn't want to inconvenience anyone but the husband went anyway and the guy was very accommodating to our request - anyways it was fixed and the next day, the husband went to his apartment again to apologise for waking him up.
i think the key is to treat people, whether they're your neighbours, colleagues, etc the same way as you would like to be treated yourself ..