Outsmarted by a 4 yr old

We had a play date with one of Beck's friends at our house. As kids typically do, he was being particularly protective and possessive of his toys and didn't want to share. Poor Rachel couldn't play with anything without Beck telling her it was his and she couldn't play with anything. We got after Beck and explained why he needed to share, etc.

Then Rachel wanted to play with his clay, and he clearly didn't want her playing with that either. So he says to her, "Do you like scary dragons?" Wondering where this leading question is going, I listen carefully to their conversation. Rachel replies, "No, not scary ones." Getting the response he wanted, Beck then replies, "Well this clay is dragon poop, you don't want to play with dragon poop, do you?" Disgusted with what she thinks she's holding, she throws down the clay and plays with something else. Beck looks at me and says, "I tried to share, but she didn't want to play with the clay." He got his way, and I had to give him credit for his creative manipulation. I then had to explain that his manipulation wasn't exactly acceptable either.

If he's doing this at 4 yrs old, what will he be doing at 17? I can't be one of those mother's who says, "Not my kid." I'll have to be the one who says, "It was likely my kid who started it."