premise: A caucasian man wearing red plaid bottoms and a black vest with large buttons with a tattoo on one arm has an upside down unicycle balancing on his mouth. hypothesis: A man is riding a unicycle.
contradiction: If the man is balancing the unicycle on his mouth, he cannot be riding the unicycle.|contradiction: A man cannot be balancing a unicycle  on his mouth and riding unicycle at the same time.|contradiction: If the rider is balancing the unicycle on his mouth, it means he is not riding it.