Like CT, for instance. Which is to say...it's illegal. If someone punches me in the mouth, and I punch them back, and a cop sees it, we BOTH get charged with the same crime....assault. If someone breaks into my house, and I beat the crap out of them, or stab them, or impede them in any way, I get brought up on assault charges, and if I use a weapon, that too. I had a neighbor who caught a kid after that kid put wholes in his tires, brought him back to his house and sat on him in the yard while waiting for the cops. He got arrested for assault, and unlawful imprisonment. Kid got hit with a fine for vandalism. Neighbors trial didn't even have a jury, just a judge, and since he broke the law, off to jail he went. Cost him 50K all said and done, and 2 months sitting in a cell.
I got pulled over for speeding once, and they saw I had a buck knife in my car, in it's sheath. First, the blade was over 3 inches or whatever, which made it illegal to OWN, and since it was in a sheath, it was considered CONCEALED.