a liar and a scoundrel
A liar and a scoundrel is a person who tells the truth, but you're too much of a pain to believe them or too lazy to do anything about it.
He said my phone was on silent, and I called him a liar and a scoundrel because I was too lazy to check.
She told me I had a smudge on my face, and I called her a liar and a scoundrel because I didn't want to admit it.
He said my dog was chasing the mailman, and I called him a liar and a scoundrel because I didn't want to move.