Exploiting other's irrationality needn't be irrational.

Tricking a bankrobber into thinking you're on his side so you can help the police capture him, for example. Using aggressive sales tactics to commit people to the idea of reading at least the "best" of the Sequences by first asking them to read all of the Sequences, for example (It's only fair, right? I mean, I'm cutting back on my wants, maybe you could do the same?) -- etc., etc..

And that's only if you're not being a dick. Nothing about rationality says you must be a good person.