Going home in a public bus exhausted after a night shift or stressful day could make one rest his sleepy head on a stranger's shoulder. Most times, the shoulder is deliberately adjusted to make you remove your head. An aggressive person on whose shoulder your head rests may even shout on you.
Of note is when a beautiful and tired lady innocently rests her sleepy head on a man's shoulder. Surprisingly, the man who would have probably reacted harshly if the head was a male's would act like the shoulder is carrying no load, might even wish his shoulder would turn to a pillow. Men some times see it as a green light.