Act I shows several features of Higgins' character. First, we find out that he is very studious and observant, taking his profession and hobby to an extreme level. He is eavesdropping on conversations, recording how people speak. When attention is brought to this fact, Higgins' seems to enjoy the attention and begins telling people in the crowd where their families come from.
We also see that Higgins' is very calloused towards people's feelings, and is very blunt in his conversation. He ignores and then scolds Eliza for her speech, also showing himself to be very judgmental. He bases his assumptions of people off their speech and their status, relying heavily on stereotypes.