Answer:
Pair is a singular noun, so when it's the subject it takes a singular verb: pair has
"This pair of chickens has a bad attitude."
previous answer misses the point entirely: it depends on how it is used, eg; She has a pair of stockings, they have a pair of stockings.
Previous amendment to this answer misses the point entirely. The question isn't asking if it's "has a pair" or "have a pair". It does depend on the context, however - If you're considering the items in the pair individually, use it like a plural subject, but if it's a single entity (pair of scissors, for example), use it like a singular subject.