Another good place is at edges of systems, particularly where they rub each other in fraught ways. What's the rule that says that computer systems invariably take on the architecture of the organizations that make them? You can predict Terrible Code Exists Here by getting a list of team names from the target (trivial -- use LinkedIn or ask anyone who works there) and then figuring out where those teams have shipped half-assed worked-on-my-machine glue code to tie their systems together.

A common example: any handoff between a marketing site (or email) and a SaaS app more complicated than "Clicking this unchanging link takes you to a login form" almost certainly involves two teams and was somebody's perceived least important thing to do that day.