No one is claiming that The Big Bang Theory is the peak of high class humor but I wouldn't say its offensive. The first example might seem offensive if you don't have any social skills but the joke is not about the eyes of Asian people, the joke is that old people, particularly in rural areas often make off hand racist comments and the awkward moments that result. The viewer is meant to relate to things they have heard their parents say rather than relating with the person reading the line.