Be all you can be Tom has this winner:

 A priest was invited to attend a house party.
Naturally, he was properly dressed and wearing his Priest’s Collar.

A little boy kept staring at him the entire evening.

Finally, the priest asked the little boy what he was staring at.
The little boy pointed to the priest’s neck.

When the priest finally realized what the boy was pointing at, he asked him

“Do you know why I am wearing that?”

The boy tentatively nodded his head yes, and asked
“Because it kills fleas and ticks for up to three months?”