I don't think there is any way to determine the magnitude of the risk. It is certainly a federal crime – 18 USC 875(c). The FBI doesn't publicly disavow the possibility of an investigation in cases that you might think are hyperbolic speech. There is the case of Elonis v. US, who was investigated and prosecuted for "making threats" – focusing on the statutory language
transmits in interstate or foreign commerce any communication
containing any threat
Defendant argued that threat "conveys the
notion of an intent to inflict harm", but the court disagreed with both prosecution and defense w.r.t. a mental state requirement in the statute. The court explores various scienter requirements, and concludes that there is a mens rea component to the crime (this is not a strict liability crime). The basis for the appeal is that defendant wanted an jury instruction read saying that "the government must prove that he intended to communicate a true threat", and what the jury was told was that
A statement is a true threat when a defendant intentionally makes a
statement in a context or under such circumstances wherein a
reasonable person would foresee that the statement would be
interpreted by those to whom the maker communicates the statement as a
serious expression of an intention to inflict bodily injury or take
the life of an individual
The court rejected importation of the negligence-law "reasonable person" standard, when the question for criminal law should be "awareness". The standard for conviction is that "wrongdoing must be conscious to be
criminal".
As for investigations, law enforcement can investigate the possibility that a literal threat corresponds to an awareness in the utterer's mind that this is a real threat. When the prosecution makes the case in court, they would have to prove beyond reasonable doubt that in the defendant's mind, he intended to make a true threat. Based on the snippet that you posted, there is reasonable doubt as to there being a true threat.