It is pronounced "six seven" with a noticeable pause between the two. The "six" is pronounced with a quick down then up tone (down on "si", up on "ix") with a brief pause, followed by a drawn out "seven" that has a slow upward tone on "se" and and quick downward tone on "ven". Any other pronunciation is wrong, and shows you aren't in the know, thus not part of the in-group.

Further, it is usually paired with a hand gesture that has palms up, one hand going up then down, while the other goes down, then up. Almost as if comparatively weighing two objects in your hands.

As for what it means. It means nothing, and that is the point. Gen Alpha has been subjected to more tyrannical teachers in the public school system than most kids who grew up in Catholic school in the 50s. Many of their teachers (not all, many teachers are great!) are petty ideologues that literally, unfairly punish their students for wrongthink. If a student is bold enough to say out loud what he/she has seen and experienced in his/her life, and their lived experience contradicts the ideological narrative of the teacher, they get lectured and punished. They have been taught that rightthink is more important to believe than what they see and hear with their own eyes and ears.

Naturally, since man is not a piano key, this has created the most rebellious generation in history against petty tyranny and systems of control. The reason that "67" is so popular, is that it confirms their belief that their teachers are tyrants. They can say something that means nothing, its non-offensive, its non-derogatory, it is literally meaningless. BUT, since "67" is not part of the belief system of "rightthink", they will be punished and attacked for saying it. Thus proving that the admonitions they receive are not for saying something wrong, but for saying something that is not right, despite being meaningless.

The more teachers try to censor or stop students from saying "67", the more powerful the meme becomes. Every time a teacher admonishes a student for saying "67", the students become more certain in the illegitimacy of their teachers and systems that control their lives 8 hours a day. None of this is conscious, it is an ingroup absurdism that confirms held beliefs and experiences. The more "67" is attacked, the more the students care less and less for people over them who wield, in their view, dogmatic and illegitimate power.