I call bullshit
When you're so sick of someone's lies that you rip them apart like a kid with a popsicle and no teeth.
"He said he didn’t cheat on the exam. I call bullshit, I saw him whispering answers to his best friend."
"She said she had no idea why she failed. I call bullshit, I know she was playing video games all night."
"He said he never broke a rule. I call bullshit, he was caught stealing candy from the teacher's desk."