Be hoist/hoistedby/with your own petard
Definition 1 of 1
Pro Tip 1/3Origin Context
Originates from Shakespeare's 'Hamlet', where 'petard' was a small bomb. Used metaphorically for self-defeat. 
He aimed to slander his colleague but was hoist with his own petard when his fabrications were exposed.
Pro Tip 2/3Archaic Usage
The phrase is old-fashioned; use it to sound intellectual or humorous when describing self-caused downfalls. 
Trying to short the market, the trader was hoisted by his own petard as the stocks rose.
Pro Tip 3/3Irony Emphasis
Best used to highlight irony, especially when someone's schemes backfire on themselves. 
He was finally hoist with his own petard, as his cheating led to his own expulsion.