Lol, it's bound to happen sooner or later. I can usually feel the difference in body posture & muscle contraction right before one lets go, but sometimes ya just can't get (your leg, arm, shoe) outta the way. Those are the times you hope for a complete miss or a solid bounce & roll off. I have one older girl, Prissy Pants, who's decided to become a shoulder chicken recently. She's pretty good about going before she gets on me or fussing to be put down when she has to go. On occasion, she'll fall asleep on my shoulder & forget where she is. I get no warning, only the pre-event grunting, holding her breath & "aaaaaah" exhale. [Honestly, she sounds like a little kid and it's hilarious.] Last night, I had Prissy Pants on my shoulder & my husband was holding our 2 new babies (who've decided to mimic Prissy & now nothing but your shoulder will do for a perch.) All of a sudden, I heard "Oh do NOT tell me you just did that!" And this is why we have certain clothes/shoes that we wear for chickens & nowhere else. No stains after 3+ years (always washed immediately), but it wouldn't matter if there were. I must admit, however, that it's not the nicest thing they do & that chicken cuddle time is generally over pretty quickly after that. Hopefully, Prissy Pants will teach the babies that GOING BEFORE getting up is better than going WHILE ON.
Hopefully the possibility of being pooped on won't keep you from holding them on your lap. They really do take on quite a different personality in the evenings as they wind down before bed. I've found that it brings out the extra cuddly side of my girls, even the ones who prefer not to be held all of the time. Those girls will sit close to me on their roost & talk to me. I think that just having frequent, human interaction like that helps them to be more sociable.
Oh but do be careful about having anyone close to your face. I can trust Prissy Pants NOT to peck me in the face, especially the eyes. I wear glasses normally, but I do trust her. And the babies are good about not pecking, too. But I'm always careful with them. I know that I have 6 chickens but only 2 eyes!