To ensure that the application is robust against all forms of input data, whether obtained from the user, infrastructure, external entities or database systems. This weakness leads to almost all of the major vulnerabilities in applications, such as Interpreter Injection, locale/Unicode attacks, file system attacks and buffer overflows.
And if it goes well, pick a book for him to read and have him pick one for you. Find something to refurbish, and meet later to do it together. Even if you don't follow through on drinks, you'll still have a new '80s windbreaker.
