To have someone's bum back into your head when you are bending over to pick something up.
"God, I nearly got headbummed by my boss when I was picking up my pen. That would have been embarrassing!"
by freddycd15 June 22, 2013
Daymmm Lisa..why be such a head bum for? I HATE YOU! Go work out those thunder thighs of yours..
by chesto dan dan June 06, 2011