For the sake of a hypothetical, let’s say the spider is only about the size of a thumbtack.
(Question inspired by the real-life reaction of someone else)
I suppose if I was startled I might make a “Yaah” sound. Then I’d blow it off my knee and let it go about its way.
If it didn’t startle me, I’d go right to the blowing it off my knee part.
I’m a guy if it makes a difference.
I would flick it off of me. female. Bees are another story…
I calmly flick the spider off my knee.
If it were particularly large or unusual-looking, or it appeared there suddenly, I might startle for a moment, but that would be all.
Kill it by smacking it hard.
Freak and find something to get it off of me with. Are you people CRAZY??? You know if you actually touch a spider with your bare hand, unspeakably horrible things will happen right?
Teeny ones, not as bad. When you can Seeeeee them (shudder) crawl? AAAGGGGGHH.
Yes, I know it’s completely unreasonable. 
I’d brush it off. Now, had the question been about a centipede, my reaction would be quite different…my strategy for them is best summed up by “cry and kill.”
Aaaarghhh! Get it off me! Get it off me! (By now it’s dead) Get it OFF me!!!
I don’t care how little it is. Or if it’s dead. They freak me out.
(Note this is an extreme reaction. Sometimes I am very calm about it all. But I’m much more likely to react extremely, most of the time.)
Depends. Am I inside or outside?
Outside, I’ll brush it off and go about my day.
Inside, well, that’s MY house. And you, as a spider, do not belong in MY house. As such, you are now dead. Sorry.
outside, whisk it off. inside, catch it and put it on a wall or toss it out a window if i am close enough and i can reach and get it open.
Spiders do not bother me in the least.
Maggots and cockroaches on the other hand need to be exterminated right away.
I’d just brush it off.
However, one time I suddenly looked down and saw a huntsman on my shoulder. That time I stood up rather quickly, took off the shirt, and waited for it to leave before I put it back on.
Flick it off my knee with extreme prejudice. I agree with the idea that spiders in the house must die. My husband wants me to not kill them because he thinks they’re beneficial, but they’re too creepy for me.
Unexpected movement on my knee usually makes me jump a little, but otherwise I’d be flicking or squishing. I like spiders to be outdoors; in my house, they are not so welcome.
Flick it gently off. No biggie. If we’re inside, catch it and put it outside.
“Ah! Hello, Mister Spider! I am afraid that I contain no tasty flies or other insects. Here, move onto this piece of paper and I’ll take you outside where you’ll find all sorts of nummy food.”
Why did I look, why did I look, oh WHY did I look?
I have a big fear of spiders but a small one I would flick off if I was outside, and kill if I was inside. Anything bigger than a thumbtack and I would be freaking out. Once I saw a big spider in my room, grabbed everything I needed and didn’t go back in for 2 weeks.
‘Hello small creature, thou art god. Here, let me help you into a more tenable location.’ Gentle relocation ensues. Widows may be treated a little roughly.
Thumbtack sized? Flick it off, and go about my business. If you get up to around quarter size, there will be some amount of startled screaming, followed by a couple of hours of heebie jeebies.
Spiiiiider!!!SpiderspiderspiderspiderGetitOFF!!! Squish
Then I spend the next 15 minutes thinking every hair or breeze that touches me is another spider.
Spiders & house centipedes are the only creatures that I **hate **and do not want anywhere near/and or on me. I don’t care about any other bugs, beetles, bees, roaches, mice, reptiles, etc. at all. Anything else I wouldn’t care if I picked it up. But spiders and house centipedes… brrr