I’m right handed. If I were to fold my hands together, like praying, the left thumb goes on top. But when I hold hands with my wife using my right hand, my thumb goes on too. We agree that it feels weird if her thumb is on top.
I recall reading somewhere that (when folding hands) righthanders tend to have the right thumb on top, and lefthanders tend to have the left thumb on top. If this is true, then you’re simply an exception to it.
I’m lefthanded: I write with my left hand, and throw a ball with my left arm. But, strangely, I bowl righthanded, and use scissors with my right hand.
Leftie, right thumb on top. When my wife and I hold hands, her thumb is usually on top. And it’s usually my left and her right.
Yup, exceptions to the rule certainly exist. I’m a righty, and I fold my hands with the left thumb on top.
Mostly righthanded, and my left thumb is on top when I hold my hands together.
Now I’m wondering if, when I hold hands with my husband, if it might be different depending if he’s on my right or my left.
Also strictly righty and when I fold my hands it feels more natural to have left thumb on top. When I hold hands with my wife, my hand is on top, no matter if she is on my right or left. Sounds sort of sexist.
I am right handed and I just tried. My natural tendency is to just fold my fingers and touch my thumbs together (who knew?) but if I push my palms together I put my right thumb on top.
I constantly fidget and twiddle my thumbs, naturally.
Not if there is mutual consent.
Like this: 
Thread winner!! 
Right-handed.
Holding my hands together, left thumb comes first.
Holding my (female) partner’s hand, use my right, she uses her left (obviously) and she’s left handed so it works nicely. Her thumb will go over mine but my wrist will be over hers. It does seem to be the way it’s done, doesn’t it, for some reason? If it’s a Male/Female couple then the man’s wrist tends to be on top. No idea why.
Height. When I hold my husband’s hand I have mine palm up, since he’s taller than me and it’s more comfortable that way. But when I hold my daughter’s hand I have my palm downwards, because she’s much shorter than me.
I’m not particularly exceptional, but I, too, have left over right.
I have left over right when I fold my arms, and when I was younger and able to do the lotus position, my left leg was above the right.
According to Wikipedia, it’s about 50-50 which thumb goes on top, though it varies in different countries, and it doesn’t say it’s related to handedness.
When I clasp my hands my right thumb goes on top. When Ms. P and I hold hands it’s usually with my left hand with my thumb on top. I’ve notice that when our son and his gf hold hands they don’t intertwine their fingers. Our daughter and her gf do.
Several years ago, I intentionally started folding my arms with the other arm on top. Now I don’t know which way I used to favor - either way feels equally natural! I’ve been doing the same for clapping, too: I usually strike my right hand with my left (if that makes sense). That is to say, I use the fingers of my left hand to strike the palm of my right. For about five years, though, I’ve been doing it the other way. It felt strange at first, but it’s getting more natural.
When my wife and I hold hands there isn’t a usual pattern, but we also often play thumb-wrestling as we’re walking so that might be a factor.