Things that people do when self-consciously observed on public transport:

:: Fake a yawn

:: Blush

:: Frown (or blush and frown combo)

:: Pick a fight

:: Pick at non-existent bits of fluff on clothing

:: Check mobile for non-existent messages

:: Bite nails

:: Scrutinise overhead adverts

:: Develop a thousand yard stare

:: Stare back