Would Graham Linehan's "If All Else Fails, Punch Him in the Balls" Be Protected Under U.S. Law?

Irish writer Graham Linehan has reportedly been arrested on his return to the U.K., in part apparently based on this Tweet that he had posted:

I don't know whether this is indeed punishable under English law; I have a hard enough time keeping track of the law of one country. But someone asked me whether this would be punishable even under U.S. law, so I thought I'd post about it.