I think the biggest "bad influence" on Ged in the whole novel is actually Jasper, the other mage-in-training at Roke. But you need to be careful with terming him as a bad influence, because it is clear that Jasper only seems to augment qualities of Ged that leads him to raise a dead spirit - his pride above all. Ged feels that Jasper made him into a fool on his very first day at Roke, and this is something that his pride forces him to remember and also gives him a desire to prove himself against Jasper:
Ged's pride would not be slighted or condescended to. He swore to prove to Jasper, and to all the rest of them among whom Jasper was something of a leader, how great his power really was - some day. For none of them, for all their clever tricks, had saved a village by wizardry. Of none of them had Ogion written that he would be the greatest wizard of Gont.
So here you can clearly see that although Jasper certainly seems to deserve some of the blame for his pride and for his "mocking smile", Ged seemed to have already been extremely predisposed to react negatively to Jasper and his mocking.