Specific coding related problems like spaghetti code and smelly code are definitely valid, but I think more than that, these are the things that give me headache.
- Lack of clear requirements.
- Lack of ownership on code.
- Lack of tests.
Purely in code, I don't like
- if-else chains, or worse, nested if-else chains.
- nested for/foreach
- methods that do too much
- methods/functions with a lot of parameters