What does "putting someone on" mean?

Solution 1:

In this case it means to tease someone, meaning 2 below (from Answers.com).

put-on n. Slang

1. A deceptive outward appearance.

2. The act of teasing or misleading someone, especially for amusement.

3. Something, such as a prank, intended as a hoax or joke; a spoof.

Note that this link is for the noun form, but the verb ("to put someone on") has the same meaning.

Sample usage:

Bill said he was going to help me fix my car, but it turns out he was just putting me on.

Solution 2:

Briefly, related sayings might include:

Are you having me on? (To kid or mislead someone )

Are you taking the mickey out of me? (Teasing or making fun of someone)

He's pulled a fast one. (To trick or mislead someone)

Solution 3:

He was worried that X was playing a trick on him, or setting him up for a little prank; in American English usage it's generally used to indicate that X is trying to get him to believe something extremely improbable (and not actually true), and at the point where he finally accepts the truth of the improbable thing, X could say "No, I was just putting you on."

Solution 4:

The NOAD describes put someone on as informal for deceive, hoax.