To be honest I am not certain of that myself. I think that Sawyer had more than one reason to run this particular con, first and foremost being that he felt incredibly uncomfortable with people not hating him anymore and trying to reach out to him (especially Kate). However, I do wonder if Jack's lack of respect (for want of a better term) for Sawyer by rifling through his stuff really, really was the proverbial straw if you get my drift?

I mean think about it: I think underneath it all, despite envying (and professing to despise) Jack for being everything Sawyer is not, in terms of being well-respected, upstanding, honourable etc...I think he does admire him a little bit too.

And his scene where he gave Jack some closure on his dad before he left on the raft was a moment where he opened up to him and showed there were no hard feelings.

Then after nearly dying while trying to save Walt, then Mike and going through the ordeal with the tailies...he finds that Jack still thinks he's shit, and doesn't respect his turf. That's gotta burn. Because despite Sawyer's posturing and 'don't care' attitude, I truly think he was hurt and angry at the way Jack was treating him.

So he wanted revenge. And wanted to take King Jack down a peg or two. Show him that he couldn't just take control of what was his.

Like I said, I don't think that was the only motivating factor for what he did, but I wonder if Jack had just come up to him and told him he needed the medicine and wanted it back, rather than going straight to ransacking his things, the outcome might have been a little different? Maybe it wouldn't have. But still Jack's actions did surprise me and I wondered if it was his jealousy over Kate that was as much a factor in his tiff, as his annoyance at Sawyer taking back the pills