Hello! I can’t tell you exactly seeing as I’ve never ordered a shirt from the new Creature Hub store before, but I own a few RT unisex shirts and some Redbubble shirts from Nova’s store.
Here’s my experience/advice:
IF YOU ARE A CHICA: …and you have big boobies, get a men’s size small. If you don’t have big boobies (or you’re a “small asian-sized human”), get an extra small, but it looks like those aren’t even available. If you’re ordering a women’s shirt and you have big boobies, get a large. Otherwise, I can’t help you. I suppose it depends on whether or not you like your clothes to be a little baggy.
IF YOU ARE A DUDE: I have no idea. Guys should know this stuff, right? In America, small is your average teen-dude size, and large is, well, large.
IN CONCLUSION: If you’re concerned about a small still being too large, ain’t much you can do. You can always shrink it :)
Also, Creatures, your store needs a size chart :)