Thorne's animosity towards Jon can be attributed to a combination of factors, including Jon's popularity and skills as a trainer, as well as Thorne's own personal history and loyalties.
Firstly, Jon's popularity among the men of the Night's Watch could have fueled Thorne's jealousy. Jon quickly gained respect and admiration from his fellow recruits, partly due to his Stark lineage and his natural leadership abilities. This popularity may have threatened Thorne's position as a trainer and authority figure, leading to resentment towards Jon.
Moreover, Jon's superior training skills would have further fueled Thorne's animosity. As a Stark, Jon had been raised in a noble house where he likely received martial training from a young age. This would have given him an advantage over the other recruits, making him a better trainer and earning him more recognition. Thorne, who takes great pride in his own abilities as a trainer, would have been resentful of Jon's natural talent and the recognition he received as a result.
Furthermore, Thorne's loyalty to House Targaryen could also contribute to his disdain for Jon. Thorne was a Targaryen loyalist during Robert's Rebellion, fighting against the Starks and their allies. Being forced to take the black and serve alongside a Stark, especially one as well-regarded as Jon, would have been a constant reminder of Thorne's defeat and the fall of the Targaryen dynasty. This could have further fueled his bitterness towards Jon.
Additionally, Jon's defiance and refusal to be cowed by Thorne would have added to the tension between them. Unlike the other recruits who may have been fearful or submissive towards Thorne, Jon stood up to him and challenged his authority when he felt it was necessary. This defiance would have irked Thorne and intensified their antagonistic relationship.
Thorne's hatred towards Jon can be attributed to a combination of factors. Jon's popularity among the men, his superior training skills, his Stark lineage, Thorne's loyalty to House Targaryen, and Jon's defiance all contributed to the animosity between them. It is a complex mix of jealousy, personal history, and differing loyalties that fueled Thorne's disdain for Jon.