It's just a CF song (though it's hilarious how it's topping charts lol)
haha thats prolly one of the bigger reasons behind the hating - they dont understand why the song is doing so god damn awesome!!
but honestly, it's not that hard to figure out is it? catchy, fun, bigbang, and the hype of a new yg girl group = chart topping success
ps.
ive noticed in various sites that some ppl are typing their name as "2en1" - prolly a simple typo (we all make them)...but the typo changes the meaning of the name completely...cos "2en1" looks like 2-in-1 or 2 and 1.
and ppl whom know of the group, but arent familiar with them at all, wouldnt even notice the mistake. and the more they see it (assuming more ppl make typos), the more they're gonna naturally think the group's name is pronounced 2-en-1.

a pointless postscript from me haha