It could just be something Jack Kirby thought was clever. He did that a lot, so a guy whose specialty is escaping from danger and who has a mother-box, he's complimented by a woman who's a big bruiser and she has a big rod. So he definitely could've meant it to be taken 'that way'.

Alternately, the Mega-Rod is the world's most ungainly metaphor for the clitoris.