I approve of the Helio kitty.
Maybe I can finally get my black adam rashguard...
A little late 'parently, but anyhow...
now i'm super tempted to do this:
If you speak polish:
That is also all I see following this link:
Rather than just being a t-shirt, rashguards are fitted and usually made of spandex, nylon or polyester. They don't keep you warm (most of them anyway); the point of wearing one is to avoid getting a rash (surprise!) from friction. I think they started as a surfing thing. They're also usually stitched so that the seams lie flat, unlike a regular tshirt.