Antonyms for "stack up against" include fall short, lag behind, trail behind, pale in comparison, and come up lacking. These antonyms imply a sense of inferiority or inadequacy in comparison to a certain standard or benchmark. For instance, if a person's performance is said to fall short of expectations, it means that they did not meet the expected level of achievement. Similarly, if a product is said to pale in comparison, it means that it is not as good as a comparable product. Therefore, using antonyms for "stack up against" can help to convey a sense of disappointment, criticism, or dissatisfaction.