Some Scottish families (certain Highland clans) often have a tartan that is considered to be theirs. If someone from one of those families were to see you wearing their tartan, they may take offence, especially if you’re a stranger and not a Scot or Irishman at all.
Other people would probably be quite pleased you’d made the effort!
If you really want to wear a kilt you could use a non tartan pattern type material and they are pretty cool looking.
And a very important thing: avoid wearing a kilt as a joke or costume.