Dammit! Now I imagine what a different kind of character Black Bolt would be if he ALWAYS communicated like this. And, just as a thought, maybe he did until he met Medusa and she found it silly? Imagine if she just one day took away his Psychic Paper Sign that relayed his thoughts and told him "Enough fooling around - you're becoming king and I will be your queen and relaying what I think is right for you to think and mean and that's the end of it!" and his sign just went "But... Me no wanna be king! Bwaaaaa!". And then he got The Stern Gaze from her and from that day onward, the poor man had to endure the Curse of the Overbearing Wife.
He really didn't communicate at ALL before he got with Medusa, which, considering they're cousins, means they met really early on. But he was kept in a soundproofed isolation chamber and forced to wear an energy harnessing suit in order to protect the Inhuman society, and wasn't allowed to leave until he was eighteen or nineteen.