A teacher at our school asked one of our students to remove graffiti that he had just written on a poster in the hall, stating that if he didn't, he'd wish he had. The kid asked if that was a threat. The teacher responded a little sarcastically, "How very astute of you" and went on down the hall. A few minutes later the principal came into his class saying, "What on earth did you say to Colin? He's climbing the walls ready to kill someone and seems to think that you called him STUPID. The mix up was soon explained and that kid actually went on to have a pretty good relationship with the teacher after discussing the meaning of the word astute.
Astute= insightful, able to assess what is going on without having it explained to you, observant.