Some people are talented at the worst things and Miss Bingley has the distinction of being really good at sarcasm. Her true colors begin to unfurl in Ch 6 with this little sarcastic barb at Mr. Darcy:

".......Miss Bingley immediately fixed her eyes on his face, and desired he would tell her what lady had the credit of inspiring such reflections. Mr. Darcy replied with great intrepidity --

"Miss Elizabeth Bennet."

"Miss Elizabeth Bennet!" repeated Miss Bingley. "I am all astonishment. How long has she been such a favourite? -- and pray, when am I to wish you joy?"

"That is exactly the question which I expected you to ask. A lady's imagination is very rapid; it jumps from admiration to love, from love to matrimony, in a moment. I knew you would be wishing me joy."

"Nay, if you are so serious about it, I shall consider the matter as absolutely settled. You will have a charming mother-in-law, indeed; and, of course, she will be always at Pemberley with you."

He listened to her with perfect indifference while she chose to entertain herself in this manner; and as his composure convinced her that all was safe, her wit flowed long.......

It continues from there all the way through Ch 9 when every time Elizabeth leaves their company she demeans and berates practically everything about poor Lizzy. I can really see the very stratified layers of society at work here as clearly the Bingley sisters are not interested in forming friendships with the "lower" Bennets and are only civil to Jane out of deference to their brother or when others are present. You've heard the saying "great minds talk about ideas, ordinary minds talk about themselves; little minds talk about other people. So much for Miss Bingley at this juncture.