My experience is that even when waiting is the norm, you can still typically interrupt as long as you “ask permission” first (outside of really formal contexts where there’s a rule against interrupting, anyway). Example of a less formal/explicit version: Raise hand slightly, go “Ah-” or “Uh...”. Example of a more formal/explicit version: Interrupt with “Can I interrupt you for a second there?” The speaker can then either let you speak (e.g. “Yes?”) or not. (Example of a less formal/explicit version: Raise hand in “stop sign” gesture or “just a minute” gesture, possibly also shake head. Example of a more formal/explicit version: “Hold on a moment, let me finish this.”)
(This obviously overlaps some with Benquo’s comment on metaconversational interruptions, though that seems to be about the reverse problem?)
My experience is that even when waiting is the norm, you can still typically interrupt as long as you “ask permission” first (outside of really formal contexts where there’s a rule against interrupting, anyway). Example of a less formal/explicit version: Raise hand slightly, go “Ah-” or “Uh...”. Example of a more formal/explicit version: Interrupt with “Can I interrupt you for a second there?” The speaker can then either let you speak (e.g. “Yes?”) or not. (Example of a less formal/explicit version: Raise hand in “stop sign” gesture or “just a minute” gesture, possibly also shake head. Example of a more formal/explicit version: “Hold on a moment, let me finish this.”)
(This obviously overlaps some with Benquo’s comment on metaconversational interruptions, though that seems to be about the reverse problem?)