[gundog]

"...does this not strain credibility to the max?

Isn't it credulity that gets strained?

[Balt]

Isn't it credulity that gets strained?

On the toilet, it's neither credibility nor credulity that gets strained.

[dmz]

usually it’s my knees that are strained. I believe the expression I used is appropriate under the circumstances. But I’m sure credulity can be strained as well.