Rep. Mark Critz (D-Pa.), one of the most vulnerable members of Congress in today's election, is a little fired up.

Check that: A lot fired up.

Critz offered this doozy of a metaphor at a rally Monday with union members, according to the Johnstown Tribune-Democrat:

"We’re going to put my size 10 1/2 shoe up Keith Rothfus’ rear end. So, when he goes back to Grover Norquist, and (NRCC Chairman Pete) Sessions, and (House Speaker John) Boehner, and (House Majority Leader Eric) Cantor and Mitt Romney, he can say, ‘Can you read this? What size shoe is this?’ because it’s going to come out of his mouth I’m going to shove it so far up there.”

Republicans highlighted the remarks Tuesday morning, with the NRCC calling Critz a "thug."

Rep. Mark Critz (D-Pa.) votes during Pennsylvania's April primary. (Todd Berkey/AP)

Critz spokesman Mike Mikus said the metaphor was intended as a joke.

“It was a joke, but I understand that the NRCC is very sensitive today because they are realizing that they threw millions of dollars down the drain attacking Mark Critz yet again," Mikus said.

Critz is a slight underdog against Rothfus in his conservative-leaning western Pennsylvania district after defeating Rep. Jason Altmire in the Democratic primary (their districts were drawn together in redistricting).

The Fix currently rates Critz's seat as "lean Republican."