Knowing some bouncers and bar tenders, they tend to have a dynamic level of skepticism. If you look 25-ish, that sort of slip probably won't deny you entry. If you look 20-ish, it may be more likely.

The difficulty here is that the incentives heavily favor allowing false negatives, and denying false positives. I know that in Virginia, the bar tenders were personally responsible if they served alcohol to anyone underage. And in a college town (where I was for quite some time in grad school), there are loads of underage kids trying to get into the bars, and the authorities would sometimes hire underage kids to test the bars.

Oh yeah, I definitely don't blame them, and I understand the incentive structure. I don't even think that I necessarily disagree with it, given our laws about drinking. It's just an irk :p