What is Cow Off?
1.
An expression of disbelief, as in "I find that extremely unlikely". A South Wales linguistic expression, especially associated with Swansea.
“I reckon Wales will beat England in the next Rugby home nations” “Cow off, they’ve got no chance."
or
“Wembley stadium should be completed in 12 months” ”Cow off, there’s enough litigation to last for the next 12 years”
See