It sounds to me like something that would be more clear in context. So here’s the context:
Mrs. Thrale then praised Garrick’s talents for light gay poetry; and, as a specimen, repeated his song in “Florizel and Perdita,” and dwelt with peculiar pleasure on this line:
[INDENT] “I’d smile with the simple, and feed with the poor.”
JOHNSON. “Nay, my dear Lady, this will never do. Poor David! Smile with the simple; — What folly is that? And who would feed with the poor that can help it? No, no; let me smile with the wise, and feed with the rich.” I repeated this sally to Garrick, and wondered to find his sensibility as a writer not a little irritated by it. To sooth him I observed, that Johnson spared none of us; and I quoted the passage in Horace, in which he compares one who attacks his friends for the sake of a laugh, to a pushing ox, that is marked by a bunch of hay put upon his horns: "fænum habet in cornu.” “Ay, (said Garrick, vehemently,) he has a whole mow of it.”[/INDENT]
A little more context: Garrick is running for office, and Johnson doesn’t seem to like him, but we’re not sure, since he gets upset over the silliest things.