Opposite: "Truer words were never spoken"
What would be the opposite of the phrase "Truer words were never spoken" ?
"I am truly grateful", said Alfred. "Untruer words were never spoken", snided Shelly.
Solution 1:
Bollocks!
…has the advantages of clarity and brevity.
Although if a phrase is required
What a load of old bollocks!
is vernacular usage.