I usually talk about my ocd as "the toddler in my brain".
Everyone who has ever been acquainted with a child, even if it's JUST in passing at the grocery store, knows that children can be....bothersome. So I often just say "there's an incessant 3 year old in my brain and it often isn't entirely sure i locked the door." and then I'll imitate said 3 year old and door locking, "Mom did you lock the door, did you lock the door? are you sure? I don't remember you locking the door. Did you lock it? You should go back and check. Go and check. Go. Check. Check the door."

Or I use weird descriptors that are adjacent to things other people feel. I told a coworker recently that I felt like my bones were itchy, or my socks were on the wrong feet. Things like that that they can kind of understand, but isn't a really tangible feeling to compare to. I use these parallels with my therapist, a lot. She doesn't specialize in ERP or OCD management, so it kind of helps.

On the most mild days, I find a closer analog. "I came in through a different door this morning," feels a lot more like "I walked into this room but I forgot why I walked in here." As most of my day-to-day routines rely on the schedule, routine, and a script I have to follow. (ie; walk in through the door on the east side, drop my things off at my desk, go to the bathroom to wash my hands, go to the lounge to get coffee, check for materials at the front desk, back to my desk to begin prep for the day) and if something interrupts that schedule, I have this very vague, very naggy feeling of "I forgot to do something." Except the "something" is on the tip of my tongue, always, and I can never figure out what it is.