Tetched

"His mind was as keen as a razor, an' as straight-edged, 'xcept jest on one subject. On that he was, so to say, a little—wal—a little tetched."

Just because he has trouble with the last verse of the Star Spangled Banner doesn't mean he's tetched. Maybe he has a mental block because you've been hammering him over the skull for three years about it.

There's a murderer about, but how can you spot him when everyone is moon-tetched?

"They ain't bin tetched or handled by any one but the Kempany's agents."

"That bullet never tetched ye!"