noun
anime freak; otaku obsessed with female characters
Derogatory slang for someone excessively into moe, especially female anime/game characters. Often used self-deprecatingly within otaku circles or as an insult.
あいつは萌え豚だから、フィギュアばかり買ってる。
That guy is such an anime freak; he's always buying figurines.
自分でも萌え豚だと思うけど、やめられない。
I think I'm a moe pig myself, but I can't stop.
オタク is a broader term for any obsessive fan, while 萌え豚 specifically targets those obsessed with moe (cute female characters) and carries a stronger derogatory tone.
萌え is the feeling of affection toward fictional characters; 萌え豚 is a person consumed by that feeling.
Compound of 萌え (moe, 'budding affection toward fictional characters') and 豚 (buta, 'pig'), implying a person who indulges in moe like a pig. The exact origin is uncertain, but it emerged in online otaku communities as a derogatory label.