In his statement, former Bangladesh programmes officer Rokunuz Zaman alleged that, on his last day with the charity, Vasey told him: "You people are very difficult, untruthful and complicated, and also very political."
Vasey, who has been head of the medical aid charity for 16 years, told the hearing: "I may well have said something to the effect that some Bangladeshis can be difficult to deal with, but this was based upon my recent experiences with the [charity's] Bangladesh programme. I could well also have said that they were political, though I do not remember doing so. I most certainly did not say Bangladeshis were untruthful."
He added: "If making sure that people do their jobs to the best of their ability and refusing to put up with second best amounts to bullying, then I am guilty."
When challenged during cross-examination on his claim that Bangladesh suffered from "pervasive and institutional corruption", Vasey denied that he believed Bangladeshis were more likely to be corrupt than people elsewhere.
The tribunal hearing in Stratford, east London, is due to finish this week.