Now, I did it last year a little while before he was moved to his paddock home and he was no trouble - he dropped when I asked, I cleaned and there was no fuss.
I decided it was beyond time to do it a few weekends back when he had his tackle out while I was washing him, and he was majorly p***ed off with me and kept trying to cowkick my arm. However, I'm pretty sure he had it out for the mares and not for my benefit (he wasn't fully erect but certainly not the usual floppy hose, and he was between two mares who were squealing and peeing all over the place *sigh*) so it may just have been the wrong moment.
I had a good feel of his sheath on Saturday just to get him happy with me fiddling around down there and he didn't fuss at all, so I'm going to give it another go this coming Saturday. Does anyone have any tips for me if he decides to be Mr Grumpypants again and not let me clean his wiener? I know how to do it but I'm wondering if anyone has tips regarding safe positions to stand in, ways to keep him from getting cross and anything else.
Otherwise it'll be a job for the vet and it might be a few weeks before they came out for a routine visit (all depends on what the other horses at the property need - with pretty steep vet call-out fees, the BO likes to get routine stuff done in bulk which is understandable).