Radiometric dating
Normal Person's Definition: “A method of determining how old something is, based on nuclear physics.”
Since it combines nuclear physics and geology, it requires a fair bit of training to do properly. Different methods have different margins of error and different ranges.
For example, C-14 is used for objects which are a few thousand years old while longer-lived radioisotopes are used for objects which are millions of years old, just as you might use a measuring tape to measure short distances and a laser to measure long distances.
Fundie Definition: “An evolutionist scam.”
You can tell it's a lie because if you get a bunch of untrained creationists to do it wrong, it doesn't work. Also, it has "error" built in. Everyone knows that real measurement techniques have no error. Worse yet, carbon-dating is totally inaccurate for objects which are older than ten thousand years.
Note: as comical as it may sound, creationists honestly believe that these are devastating critiques of radiometric dating. Unfortunately, to the average layperson who struggled through high-school science, they might very well be.