All the good puns are taken, so I'm stuck with advice. Oh well.

As most have said, a dirk these days usually belongs on the hip of drum major. I've seen plenty of pipers and bands sporting them, and almost 99% of them look a little goonie. If I see someone wearing a dirk with daywear, I usually assume that they're a beginner piper or with a parade band - the latter invariably in spats and short-sleeve shirts, ugh. If they're not a piper, I assume they're crazy and try not to bother them while they stare at the sheep trials.

That said, if not in Number 1 dress or Patrol (in the military piping context), I think it works with black tie, but only if you're at some sort of Highland society event - not your brother's wedding where everyone else is in a dinner jacket or tux. Also, I think if you're not wearing argyle hose or buckled brogues, you shouldn't be wearing a dirk. People disagree about the Prince Charlie and a dirk, but I refer doubters to the old pictures of Bob Hardie that accompanied his ads - I think he was wearing a PC with a dirk, fly plaid, buckled brogues, AND a balmoral and he looked awesome. Of course, that was in the 60s, he was a Scot, and one of the greatest pipers of the age. So take it for what it's worth.