The word "stupefyingly boring" can be a harsh way to describe something that lacks interest or excitement. When searching for synonyms to replace this phrase, a few options come to mind. For example, you could use "tedious" to describe a task or activity that's dull and exhausting. Alternatively, "monotonous" works well for a repetitive or unvarying job. Another option is "mind-numbing," which conveys the idea of something that puts you to sleep or leaves you brain-dead. Other synonyms to consider include "dreary" or "tiresome," which express a similar lack of enthusiasm. Overall, it's essential to choose the right word for the context in which it's used.