Your organization should have a coding guidelines/standards document that's periodically updated with input from the development team. That document can spell out specifics, like: how to name variables, how to format code, and so on. The document should also explain the values that the organization expects programmers to adopt in writing code, including the relative importance of things like readability, maintainability, correctness, efficiency, and adherence to standards.
Code reviews should be conducted using that coding standards document. If the coding standards say that programmers should prefer readability to brevity when the two are in conflict, then you'll have some support in arguing against the "clever" code. If the standards don't say that and you think they should, then you can argue about it in the abstract at the coding standards meeting rather than trying to figure it out when somebody's ego is on the line.
Ultimately, it does sometimes come down to a judgement call, and in those cases the final word should go to the person that's ultimately responsible for the code and/or product. That's usually someone like a senior developer, technical lead, project manager, or director of engineering. If you're the guy in charge and you feel that certain code isn't sufficiently maintainable, you shouldn't be afraid to say so. You can be diplomatic about that:
Sam, I'm impressed with your ingenuity here, but I'm concerned that it
may be just a little too clever. I'll need you to be working on new
development a year from now rather than maintaining this, and I'm
concerned that whoever does have to maintain it may not fully
comprehend its awesomeness. I know you hate to do it, but I'd
appreciate it if you'd go back to the straightforward implementation
that we discussed.
On the other hand, if you're not the guy in charge, then the best you can do is explain your position clearly and try to convince the rest of the team. If you're not getting support from the manager, then accept that it's not your call and move on.