Well obviously you know that! @Colin McCoire

I conjecture the next person is annoying (koff-koff)

Moi!? I'm the nicest cousin you've got!

I conjecture the next person loves riding horses.

Sadly no. And you are a little annoying.

I conjecture the next person is a Slytherin

That's a trick question

I conjecture that the next person knows how to use power tools like a lawnmower or something.

Unfortunately yes, I did a lot of chores back home so I know how to mow a lawn without magic (so neighbors wouldn't get suspicious)

I conjecture that the next person is lactose intolerant

Please, I love milk but my tummy doesn't.

I conjecture the next person who doesn't like hot dogs

Please, I love milk but my tummy doesn't.

I conjecture the next person who doesn't like hot dogs

I used to like them a lot, until one of my sisters told me what they were made of. Now it's a bit harder to swallow.

I conjecture that the next person has tried firewhiskey before

I wish.

I conjecture the next person who hates spinach

Yes. Yuck.

I conjecture that the next person is deathly allergic to something