Who was the boss?

I believe the title referred to a refrain commonly uttered by frustrated parents. It is a rhetorical question, meaning it is not really a question but a statement. The parent saying "Who's the boss?" is basically telling the kid "you're not in charge -- I am."

I think it was used as a title because it is kind of like a double entendre, in that it could be that the parent saying "Who's the boss?" really isn't the boss. In other words, someone else might really be in charge.

From wikipedia: In early development, the series was titled You're the Boss, in reference to Angela employing Tony and the highly unusual gender role reversal. Before the fall 1984 premiere, the producers changed it to Who's the Boss?, an open ended title which hinted that any one of the leads could get their own way and be the "boss".