I have been a church organist since the age of 16, so I have seen some horrendous behaviour in the thousands of funerals I have played for. The worst was probably the funeral of a child, who had been chronically ill for most of his short life. The father turned up drunk and stoned and at one point, we had to evacuate the room at the funeral parlour while the grandfather 'calmed' the father down. I believe it came to blows. That was also the funeral when the minister, in full robes, kept talking about 'the Christian myth'
. As he was a Church of Scotland minister, and chaplain of the Sick Kids' hospital, that was very weird.
At the wake after DM's funeral, my DF went off on one of my friends because he thought the friend was hitting on me because he gave me a hug. DF was very socially inept and was annoyed that I refused to have him called the widower during the funeral service because he and DM had been divorced for quite a long time. Oh, and DF also accused me of trying it on with the minister who was doing the funeral service. DF was at my house when the minister (who I had known since childhood) came and gave me a hug.
The most awkward funeral I ever attended as a mourner had to be my BIL. I was separated from XH at the time, but he hadn't told people. Everyone wondered why I was there, but not sitting with the family at the front.
I have also, on occasion, turned up to play for a funeral and discovered that I could also have been a mourner. Very tough.