You perv.
When going up, in case the girl falls, the guy is behind to
catch her.
When alighting, again if the girl falls, she can at least grab
the guy in front of her to steady herself. 
machiam taking a bus is as dangerous as climbing mount
everest....
if the ger u dating fall so easy.... i think u better take her
go see some specialist... 
Anyway, why so serious....
then again... if the ger wearing super short skirt, would u
still walk after her when boarding the bus?