I guess it's cultural to some extend. Never worn one myself and almost everyone I trained with in Denmark did the same. Many girls just wear a sports bra under the gi. But we're also in general very comfortable with being naked around each other.

I remember an incident where a Finnish competitor got a written warning from the IBJJF when he dared to take off his hoodie from under the gi top in the bullpen area... Feels so weird in our cultural context.

I've always preferred wearing a rash guard under my gi. I simply find it more comfortable both for myself and I'm more comfortable knowing my training partner doesn't have to endure my slimy sweaty body when it opens during rolls. Especially for women that train with me. I'm interested to know what the Jitsu community feels about wearing a rash guard under your gi, and for your training partners wearing/not wearing one. Should it be mandatory? Why/why not?

I don't wear a rashguard under my gi. I tried it once or twice and felt it makes me get to hot. Christian, I cant believe people actually complained about that. At my gym most guys train without the rashguard under their gi. When done training we usually take off our gi tops because we are hot.

Hot as in warm or as in sexy?

Who doesn't love removing suspect short hairs from the back of throat mid roll?

I didn't prefer it when I first started but over the years I've come to prefer wearing one to not

I prefer with underneath,but that's just a comfort thing for me. I also wear spats. Gi pants start klingons to my legs when they get sweaty. But I also prefer when my training partners wear rash guards. Mainly because we generally switch between gi an no gi while we're sparring and I prefer not having someone's sweaty hairy chest in my face.

I don't care if anyone wears or doesn't wear a rashguard under the gi top. I started wearing one under my gi top after a few ringworm and MRSA infections. (2007 or 2008 or so) Decided that people are nasty and at least it offers me some protection even if limited. Man I used to overheat in the rashguards too. I'd have to cool my ears off with something cold for awhile. Now I'm used to it.

I remember I was once in a gym in the US with a large matspace. I dropped my jacket at one end and started walking across the mat. As I had almost reached half way across, I realized that pretty much everyone was watching me, mouths open, in despair - whispering to each other, not believing that I would do such a thing (exposing my nipples and all!!!). It was extra awkward as I couldn’t figure out if I should keep going, speed up to reach my destination of the changing room or I should turn around, run back, put on my gi jacket and then take the same walk across the mat again. Very difficult cultural situation for a tourist like me.

I guess it's cultural to some extend. Never worn one myself and almost everyone I trained with in Denmark did the same. Many girls just wear a sports bra under the gi. But we're also in general very comfortable with being naked around each other. In the US, I have been pulled aside a few times and asked to put one on. And Odin forbid those times I've taken off my gi jacket on the mats there, oh my oh my.

I remember I was once in a gym in the US with a large matspace. I dropped my jacket at one end and started walking across the mat. As I had almost reached half way across, I realized that pretty much everyone was watching me, mouths open, in despair - whispering to each other, not believing that I would do such a thing (exposing my nipples and all!!!). It was extra awkward as I couldn’t figure out if I should keep going, speed up to reach my destination of the changing room or I should turn around, run back, put on my gi jacket and then take the same walk across the mat again. Very difficult cultural situation for a tourist like me.

That said, I've only been training this sport for 16 months and I've already accidentally grabbed a dick and put my finger in someone's mouth while rolling (not on the same day!).

That said, I hate when people wear a t shirt under the gi, especially if it's loose fitting. i'm always getting my fingers tangled up in it.