I've been wondering if it would make sense to have a lightweight way of expressing frustration at a given bit of source code, in a way that's collected and aggregated.

It seems like this could be useful for prioritizing technical debt, although it's likely more complicated than a naive ranking). Surfacing the info during code review might point to areas that need additional attention. Overall trends (for the group and for individuals) might help give a manager a better sense of the health of the team.

Of course, one would have to be very careful about the social dynamics of it all; in particular, tying it to blame seems fraught.