First, you need to experience some form of displeasure. Whether that be losing your job, getting a bad grade, or getting ganked in Stranglethorn.
Step2
Gently turn the corners of your mouth down and furrow your brow. When this is done, and the emotion is felt, your ears will begin to droop naturally.
Step3
Make a sound, preferably "Mwoop".
Tips & Warnings
In step two, it sometimes helps to produce the effect known as "puppy dog eyes".
The sound "mwoop" can be expressed in sadness or in sympathy. For sadness, it's desirable to say "Mwoop...". For sympathy, it's more of an exclamation: "Mwoop!"
If you choose to add puppy dog eyes, remember that the point of this expression is the MWOOP, not the eyes.