Wet bet can be best described as whatever you want it to mean
If someone said "I just found 100$ dollars" your response would be "that's a wet bet" or if they said "I just lost 100$ your response would be "dang man that's a wet bet"
noun: a Wet Betty is the step sister of the wet willy. a Wet Betty is performed by sucking your finger tip, and swirling it around in someone's exposed cleavage and yelling "WET BETTY." This can only be used on EXPOSED cleavage; no reaching down t-shirts, turtle necks, or sweater vests!