My eye!
Definition 1 of 1
Pro Tip 1/3Skepticism Expressed
Use 'my eye!' to express doubt about something you think is untrue or exaggerated. 
A flying car? My eye!
Pro Tip 2/3Humorous Tone
'My eye!' often carries a light, humorous tone, rather than harsh criticism. 
'He's a genius, my eye!' she chuckled.
Pro Tip 3/3Informal Usage
This expression is informal and best used casually among friends or in light-hearted contexts. 
You won the lottery? My eye!