Antonyms for the term "most endorsing" include disapproving, criticising, condemning, opposing, rejecting, and disproving. When someone disapproves of something or criticises it, they are clearly not endorsing it. Similarly, when someone condemns or rejects something, they display a negative attitude towards it. Opposing something implies that the individual is standing in direct opposition to it, thus indicating a lack of support. Finally, disproving is a synonym for debunking, which means to prove something false. These words are the opposition to endorsing, indicating a lack of approval or support for a concept, product or service.