The word 'abysmal' suggests a very strong level of disapproval or disappointment regarding quality. His manners were abysmal, far beyond what we could overlook.
Pro Tip 2/3
Intensity Amplifier
Use 'abysmal' to emphasize the severity of a situation or the extent of poor quality. The conditions in the refugee camp were abysmal, much worse than reported.
Pro Tip 3/3
Not for Slight Dislikes
'Abysmal' is reserved for extreme cases and shouldn't be used for mild dissatisfaction. It would be an overstatement to call a mildly unpleasant meal 'abysmal'.