1. because someone else is nearby eg; a woman is making the tea while you're sitting at the table.
2. because you really shouldn't be doing it there eg; work.
3. because if your missus finds you looking at other women you'll get an earfull.
if the person you are trying to hide your wank from becomes suspicious, the spunk hunt is on. you must find and destroy all evidence before they do or else you'll be in trouble.
1. 'do you want carrots or not?'
'no thanks' (knowing the wank was undetected)
2. 'have you called mr. evans yet?'
'nope' (knowing the wank was undetected)
3. 'what's that magazine?'
'men's health' (knowing it was penthouse magazine)