I'm not sure if you're trying to say my Luna shirt is some kind of meme, or you're just pointing that out because it's related to shirts and internet. Anyway, I think meme shirts are quite stupid.
no, but MLP is very pop-culture-y
subtle references are just fine in my opinion, though
for example, a shirt colored like this:

with a small design near the bottom of it such as:

would be totally acceptable to me
no stars though, and no cat