We usually see "felony"....or a real crime.
From Gorsuch’s controlling opinion:
“Having said this much, it is important to acknowledge some limits on today’s holding too.... Vagueness doctrine represents a procedural, not a substantive, demand. It does not forbid the legislature from acting toward any end it wishes, but only requires it to act with enough clarity that reasonable people can know what is required of them and judges can apply the law consistent with their limited office. Our history surely bears examples of the judicial misuse of the so-called “substantive component” of due process to dictate policy on matters that belonged to the people to decide. But concerns with substantive due process should not lead us to react by withdrawing an ancient procedural protection compelled by the original meaning of the Constitution.
Today’s decision sweeps narrowly in yet one more way. By any fair estimate, Congress has largely satisfied the procedural demand of fair notice even in the INA provision before us. The statute lists a number of specific crimes that can lead to a lawful resident’s removal—for example, murder, rape, and sexual abuse of a minor. Our ruling today does not touch this list. We address only the statute’s “residual clause” where Congress ended its own list and asked us to begin writing our own.
Just as Blackstone’s legislature passed a revised statute clarifying that “cattle” covers bulls and oxen, Congress remains free at any time to add more crimes to its list. It remains free, as well, to write a new residual clause that affords the fair notice lacking here. Congress might, for example, say that a conviction for any felony carrying a prison sentence of a specified length opens an alien to removal. Congress has done almost exactly this in other laws. What was done there could be done here.
But those laws are not this law. And while the statute before us doesn’t rise to the level of threatening death for “pretended offences” of treason, no one should be surprised that the Constitution looks unkindly on any law so vague that reasonable people cannot understand its terms and judges do not know where to begin in applying it. A government of laws and not of men can never tolerate that arbitrary power. And, in my judgment, that foundational principle dictates today’s result....”