Bill O’Reilly used this as his word of the day in one of his recent shows, and he said something to the effect that it merely referred to clothing babies once wore and was not an insulting term. The dominant theme from an internet search is that it is “…a mild slur, meaning someone who is weak; a sissy. It is almost universally applied to men.” The term originated with the clothing of babies “…in one piece suits, a shirt and pants with snaps or buttons around the garments’ middles to allow easy access to diapers.” It was a “union suit” if it had long pants or a “pantywaist” if it had shorts. It might be called the trademarked “Onesie” today. Regardless, the consensus (and I often think things determined by consensus don’t turn out to be all that accurate) is that the term “…is an insult, so should be used with care.”