When you are just a small amount under 100 percent sure of something, but you recognize slim possiblity that you are wrong. You are as sure of something as a condom is preventative. You are 99.9 percent sure.
"I'm condom sure that global warming is real."

"Are you sure you're ok to drive home? Are you condom sure?"
by XombiEZ September 8, 2011
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