A guy who seems sweet and kind because he flirts and gives you unwarranted attention, but who is actually a creepy predator/pervert on the prowl for some new (usually young) girl of whom he can take advantage. A groundhog spends the majority of their time being an underground gets labeled as such because of the amount of time they remain underground sleezes. The best defense against groundhogs is to chase them out of their holes and expose them.
When a senior football player flirts with a freshman cheerleader, he is a groundhog.
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