Suppose I don't?

Suppose I don't?

What would the consequences be if I did not do (whatever you just mentioned)? Implies that the speaker either believes they are right not to do something, or else they are suspicious of the other person questioning them about it. A: "I'm warning you for the last time to take that money to the bank and deposit it!" B: "And suppose I don't? What exactly are you going to—report me to police?" A: "We need to report those earnings so we can pay taxes on them later." B: "Suppose we don't, though? Would anyone ever find out about it?"
See also: suppose

Suppose I don't?

 and Supposing I don't?
Inf. And what will happen if I don't? (Said as a sort of threat. Not usually with question intonation.) Bill: You'd better get yourself over to the main office. Tom: Suppose I don't? Father: You simply must do better in school. Tom: Supposing I don't? Father: Your clothing and personal belongings will be placed on the curb for the garbage pickup, and we will have the locks changed. Next question.
See also: suppose