To laugh up your sleeve is to laugh quietly and secretly. Of course, when you laugh secretly, you are ridiculing the person, but you don’t want him or her to realize it.

• The audience seemed to enjoy the performance, but most of them were laughing up their sleeves.

Most of them didn’t enjoy the performance at all, but instead of making their displeasure known to the performers, they chose to hide it by laughing up their sleeves.

• Susie pretended to admire the artwork, but I knew that she was laughing up her sleeve.

According to scholars, this expression has been in use since the 16th century. In the 16th century it was fashionable for English men to wear shirts with large fluffy sleeves. Because the sleeves were too big, people could easily hide their faces in them. And they used to do it when they wanted to laugh or frown secretly.

Look like death warmed over / feel like death warmed over

To look like death warmed over is to look terribly ill. When you feel like death warmed over, you feel extremely tired.

• Suma has been ill for several weeks. No wonder she looks like death warmed over.

• I haven’t had any rest in a long time. Actually I feel like death warmed over. (= I feel extremely tired.)

• I haven’t slept in days. I feel like death warmed over.

• Poor Tom looked like death warmed over when I saw him at the hospital.

The expression look like death warmed up has the same meaning.