Darcy had barely finished insulting the lady to Bingley, when she suddenly stood before him.
She looked him up and down, with a look of mingled disbelief and disgust, shaking her head. Then she turned her back on him and walked away.
After they became engaged Darcy asked, 'if you were so angry at my initial insult, why did you not say something?'
'Since we had not been introduced it would have been improper of me to speak to you. I thought you were intelligent enough to interpret a look.'
Since Darcy had immediately apologised, Elizabeth had been correct.