Does the word "altitude" refer to the character's height? Is it a common expression?
"Altitude" actually refers to height or elevation, i.e. the height of something in relation to the ground or sea level. In this case, the speaker is making a joke that the length of the high heels her friend is wearing may be affecting her judgement, due to the decreased oxygen level one finds at high altitudes. Ex: The plane is flying at an altitude of 35, 000 feet above sea level. Ex: Oxygen levels decrease at high altitudes, so mountain climbers often carry oxygen tanks with them.