85 times out of 100, it needs to be a fantasy of some sort, or an object related to the fantasy.
If it's a fantasy, it is predominately my laying on a bed and recieving extremely sloppy oral sex from an attractive young woman in either a school uniform with white opaque tights and black dress shoes, or an ABDL footed sleeper, culminating in my ejaculating in her mouth and her struggling with it.
Either that, or I am watching the same girl on the bed, masturbating herself, and wearing a mask because of some medical need.
And usually the girl is based heavily on a girl I knew in real life who made me comfortable with my medfet.
If it's an object related to fantasy, it is a mask, which is my medfet. Throughout my life, I have been attracted to female patients needing to be masked. It started with the "black beauty" anesthesia masks of yore, but largely pivoted to protective masks that we see on transplant patients and for COVID and other transmissible things. The sexiest masks to look at on their own, without a girl wearing it, for me are half mask cartridge respirators, usually with P100 cartridges on the sides, and usually black, with a thick halo strap set-up. And I like looking at it on the inside, as if it is ready to be put on me.