The wait staff and by others at the table. I think there's a subconscious perceived status thing that just makes interruption less likely for "white" men. Granted, this is just my perception. Data would be good. I should probably search the social psychology literature.
Interruption might be partly due to mismatch in visual cues. People look for non-verbal signs that a person stopped talking. Maybe those misfire because of cultural differences? If true, this should be especially pronounced in group conversations.