naysayer (n.)

• anomaly
• brawler
• crosspatch
• defeatist
• defendant
• denier
• diehard
• disputant
• dissenter
• dissident
• freak
• individualist
• litigant
• misfit
• negativist
• nonconformist
• objector
• obstructionist
• oddball
• opposer
• pessimist
• plaintiff
• protester
• quarreler
• resister
• sceptic
• scrapper
• sport
• wrangler