Possible Clues:

• One may be suppressed in class
• Fail to stifle one's boredom
• ''Ho-hum!''
• Jaw-dropping opening?
• (I'm bored)
• Yachtswoman has no stomach for sign of boredom
• Show lack of interest, in a way
• Be open-mouthed as new fashion gets taken up
• Sleepy behavior
• Open up North Street from below