Not your thumbs, but any of the four fingers on each hand. It’s odd - neither I nor anyone I speak to can bend the last joint of their figners without bending the second-to-last. Is there a good reason for this?
This is one of those IMHO threads… but I’ll answer it before a happy Mod gives it the bounce.
No. I can’t. But I know several people who can.
I can bend just the middle joint leaving the last one straight. I can do this on all fingers, one at a time or several fingers in any combination.
Not one of my friends who could just bend their last joint could do this.
I can, with my index fingers - and I can do what Seven mentioned with all of 'em.
I’m just weird, I guess.
I can with seven of eight fingers. Though if I do it for too long it hurts and sometimes it feel like the little fingers are frozen that way (eeeeek and ouch).
Just another weirdo
I can do it wither all my non-thumb fingers, though for my pinkies it may take a couple tries.
I can do it if I hold the bottom joint rigid. I reckon that with lots of practice I could do it for real
I can do it with all of my fingers. It grosses everyone out. I can do them all at the same time, or individually.
I don’t get it 
Bend, like how?
1 1/2 out of 8 here.
…just doing my part to add to scientific knowledge.
Just now I tried it for the first time since who-knows when. Yep: I can still hold my fingers rigid and bend them at just the uppermost joint. In the fourth grade this gave me a sort of limited claim to celebrity.
I can also flex my elbows so that they bend “backwards” to a slight degree. At least around St. Louis, being able to do such things with your fingers and elbows is referred to as being “double-jointed”.
In high school I had a classmate who could bend his legs “backwards” at the knee. He was on the swim team, and liked to gross out competitors from other schools by doing that just before the starting gun in a race.
Just now I tried it for the first time since who-knows when. Yep: I can still hold my fingers rigid and bend them at just the uppermost joint. In the fourth grade this gave me a sort of limited claim to celebrity.
I can also flex my elbows so that they bend “backwards” to a slight degree. At least around St. Louis, being able to do such things with your fingers and elbows is referred to as being “double-jointed”.
In high school I had a classmate who could bend his legs “backwards” at the knee. He was on the swim team, and liked to gross out competitors from other schools by doing that just before the starting gun in a race. There’s nothing like making the kid you’re racing against want to vomit to give you an edge.
Oh ok, now I understand. I can do it with my index fingers but none of others.
I can do it with all my fingers. I have a freind who can do it too, so I guess it’s not that rare.
I can only do the last joint trick with the index finger of my primary hand. The second joint trick can be performed once again only on my primary hand with all the fingers except the baby finger.
I can also bend my thumbs backwards to 90[sup]0[/sup], however, I cannot touch the middle of my palms with the tip of the adjacent thumb.
I can flex just the top joints of 7 of my fingers. For some reason the pinky finger of my left hand won’t do it, even though I’m left-handed. It’s good for doing cat impressions.
I can do each finger on the last joint and also each finger on only the middle joint. I remember back in school, someone else did it and i couldn’t for the life of me! but i practiced, and eventually got the hang of it, seems once it’s learned it sticks… i haven’t tried it in years but can still do it.
speaking of digit tricks - it always amazes me how people can spread out their toes…i never could, but then that might be because the 2nd + 3rd toe on each foot is joined together (i do have a pic if anyone’s curious LOL) … you’d think i’d still be able to stretch the others out though, but nope! If i try and stretch my big toe out it moves up instead
I can bend all my fingers at the end and middle joints. I used to do the former to gross people out when I raked my hands across their skin. 
This is a sort of survey, so I’ll move this thread to IMHO.
bibliophage
moderator GQ
Many people can do this. This is something doctors test routinely in people who klutzily cut their fingers with axes, knives, etc. to see if the tendons are or are not intact.
It is easier to do if you hold the neighbouring finger still.
Many people lack the tendon, naturally, to bend the last digits of their pinky. Lots of people can do this with one pinky only, or not at all, since both tendons often are not present. (Another anatomical variation, many people lack the palmaris longus muscle when they flex their hand).
It is easier to grip objects when both the distal and proximal pharyngeal joints flex. In terms of practical use, it makes sense to bend both joints at the same time. The flexor carpis superficialis and profundus tendons that bend the “body” and “tip” of the finger are connected by an intriguing pulley system which also makes it hard to bend just the distal joint, if you don’t think about it too much and try to bend it separately
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Thanks to years of flute playing, I can do it will all fingers (in fact, my pinky used to get stuck in that position after playing too long 
). I can also bend just the second to last without bending the last, which grossed people out to