Possible Clues:

• Not a forward way to have one's fling
• Not likely to make the first move
• Unassuming
• Short at the poker table
• A this sort of blow is pale
• Reluctant to meet people, say
• Hesitant to ask that pretty girl to dance, say
• Nervous or timid in company
• Slow to mix, say
• 'Lacking self-confidence, timid (3)'