I mean, there's no legal definition of "tailgating" right? 5 or 6 people standing around a truck isn't against any current policy in Knoxville. If you try to have 30-40 people together, you'll likely draw attention, but I can't imagine they can crack down on groups smaller than 10. If an officer comes up to you, simply say, "Hello officer. No, we aren't tailgating. We're having a nice day enjoying the weather outside." I can't think of any legal authority the city has to breakup something like that.