When periods of unexpected inflation comes, consumers of any kind of goods and services are the most affected here because with the same amount of money we used to buy a number of goods and services before inflation, won't be enough to buy the same things during inflation periods. That said in different words, prices get higher.
During unexpected inflation periods, the most harmed people are those who are paying a loan with adjustable interest rates because as its own name indicates, it is adjusted periodically based maybe on the economy. If there's inflation, it means that people are going to have to pay more money than they used to. Also, elderly people who have a fixed income get harmed because of what I explained before, prices get higher and the won't be able to cover all their needs with the same amount of money.
To summarize the answer is: People with adjustable interest rates and elderly with fixed income