Board Thread:Questions and Answers/@comment-39106664-20190420011352/@comment-35757757-20191225030740

Mettaton has only been referred to in the game with MALE pronouns

His femininity could be explained just by saying he’s effeminate

The definition of effeminate is (and I quote from Dictionary.com):

“(of a man) having or showing characteristics regarded as typical of a woman; unmanly.”

There’s a word for it. There’s your explanation

He’s just a feminine guy