In the case report [here](https://www.ncbi.nlm.nih.gov/pubmed/9140329), the guy drank 2-4L of soda per day for 6 months.  The full article is behind a paywall, unfortunately.

And [this other guy](https://www.nejm.org/doi/full/10.1056/NEJM200305083481921) drank 8L of Ruby Red Squirt every day for months before getting dermatological symptoms of excessive bromide.