"I got the bill for my surgery. Now I know what those doctors were wearing masks for"

This quote is a funny method of expressing the shock of receiving a big medical expense. The speaker is indicating that the doctors were using masks to hide their amusement at the expense of the surgical treatment. The speaker is likely feeling overwhelmed by the quantity of money they need to pay and is utilizing humor to cope with the circumstance. The quote also suggests that the speaker was uninformed of the expense of the surgical treatment prior to receiving the expense, which might be an indication of naivety or absence of financial literacy. Overall, this quote is a humorous way of revealing the shock of getting a large medical bill.