Ask him specific questions where eventually he will figure out himself that he's wrong. Whether he admits it or not depends on how mature he is.
You might start with...
Really? So bucks are the only sex of deer that have dew claws? I didn't know that!
If he say that they are, then the next time you (or he) kills a doe, and you point out the dew claws then ask him if this one is a mutation. Hopefully it won't get to that.
If he says that they both have them, then ask him why it's only evident in a buck track. Soem believe that it's because bucks are bigger, but what about a 3+ year old doe? Here in Illinois we see many does that are in the 160 to 200 pound range. Or what about a 1 1/2 year old buck who DOESN'T leave a dew claw track and a big, old doe that does?
Fact is, although one can make an educated guess based on size, location, and track pattern about what sex of deer made it, the only true way to tell is to either see the deer standing in the track or to see in the deer's bed if there is a urine mark (many bedded animals will urinate after getting up if they've been down a while and not spooked). If it's in the middle of the bed it's a buck, and if it's on the edge or outside of the bed it's a doe. You really need snow for this to see where the tracks are in relation to the urine mark and the bed.
Offer No Apologies.....
NRA Endowment Life Member