What is Sebastard?
1.
Anyone named Sebastian who happens to also be a bastard (literally or figuratively)
dude1"whats that asshole's name again?"
dude2"uhhh sebastian I think."
dude1"you mean sebastard"
See
2.
someone who is being mean, rude, bastard, etc
"god jen you are being a real sebastard, why did you eat all of my tootsie rolls?"
See