Any analogy, metaphor, etc where the person speaking/writing is attempting to use a common phrase but messes it up by either mixing multiple common phrases, or simply replaces key words in the phrase with incorrect words. The most important aspect of a ruddism is that they are not done on purpose. The person must think they said it correctly.
Examples of a ruddism:

"A bird in a hand is better than two bushes."
"You have enough to do. I don't mean to throw more worms on the fire."
"She was green with ivy."
"You can't teach a dog old tricks."
"That's just my cross to burn."
"You can lead a gift horse to water, but you can't look it in the mouth."
"Six of one. Half of the other."
by He3Times July 28, 2017
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A sentence or phrase comparing a recent experience to a smart or witty sentence that would be said in a movie starring Paul Rudd.
Cliff: ...That's almost as gay as the Miley Cirus PSA telling us not to call things "gay".

Luke: Dude, nice Ruddism! That sounds like something out of a Paul Rudd movie!

ref: "You know how I know you're gay? You listen to Coldplay" -40 Year Old Virgin
by Mimi227 December 18, 2009
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