I worked in HR, so I sometimes had to sack people. I always tried to do it tactfully and well, out of consideration for the person I was sacking, but it never became easy or enjoyable and indeed, if it had I'd have packed in the job.
The worst thing I ever had to do was to visit an employee in her early forties, who had given birth prematurely and the baby had died after a few hours. She had no other kids and felt (probably correctly) that it was her last chance and she was consequently heartbroken. I'd just gone to see how she was doing, but I ended up spending most of the day trying to console her, and looking at her mementoes, such as the little baby grow he'd been put in, and stuff like that. My kids were very young at that time (our son was just a few months old) and all in all, it was a day I'm not in a hurry to repeat.
My other nightmare was the day of the 7/7 bombings. One of my London based staff didn't turn up in the office and we couldn't get hold of her on her mobile. Finally, at about 4 in the afternoon, somebody found a picture of her on the Evening Standard website, covered in a blanket and being escorted to an ambulance; she texted us about an hour later. She had been in a train travelling in the opposite direction to one of the bombers and had inhaled a lot of smoke after the blast. Being asthmatic, they had taken her into hospital to check her out, but they released her later in the evening. I have never felt more relieved than the moment I saw the photo of her on the Internet.