A logical fallacy
also called a false dilemma
. This is when you give two choices--a dilemma
(of sorts), but fail to point out that there is at least one other choice.
"Either you're for us or you're against us"
"Are you a Christian or an atheist?"
"Get in the car now! I don't have time to stand here all day!"--This one is totaly true--but the implication is false.
"If Ralph hasn't finished that report yet, then he's a lazy bum"--This one could be true, but I would suspect that a third case is possible.