“I hope so, Commander. For your sake. The Emperor is not as forgiving as I am”
dah dah dah daaah dah dah dah dee dah
Also,
“Jabba. This is your last chance. Free us or die”
Jabba thought it was a joke. We the audience and Han probably thought it was a bit of bravura, or Luke stalling for time. But Luke was just making a simple statement of fact.