This happened a couple of years ago....

My neighbour got a new kitten, he was lovely and he used to spend alot of time with Furball (I think she got quite maternal), she has been spayed so I didn't have any concerns to start off with, but then he started to really pester her and spraying my front door (not pleasant).... So I go down to see his owner as Furball was starting to show signs of stress and was loosing weight.
The conversation went a bit like this:-

Me:- I'm sorry to inform you but your cat has started to really harass mine now, and he is spraying my door so I was wondering if you had considered getting him cut?

(Normal moggy type cat so I didn't think that he had a breeding program or anything)
Neighbour:- What do you mean by that?

Me:- Castrated......

Neighbour:- Oh I see thats ok he has already been done.....

Me:- (very confused at this time) Oh ok, in that case things should settle down soon enough.

As I was finishing my last sentence said kitten decided to have a bit of a roll right in front of us, and very kindly flashing two quite large testicles....

Me:- Ummm are you sure he has been done?

Neighbour:- Yup

Me:- In that case I suggest you take him to the vets as there is something going on there.

Neighbour:- Oh that, that's just what is left....

At this point I realise that I am wasting my breath (they were 100% testicles). And sure enough we had an influx of little black kittens turn up in our nieghbourhood.
A while later my neighboor said he was off to the vets to get said cat castrated, and in response to my hang on didn't you say he was already done? Yeah but I thought you were talking about his jabs....