When to be frank in an interview process when the company is taking much longer than expected to respond about my application?

I had an second round interview for a company in the drinks and beverages industry based in Brussels 5 weeks ago.

I was told to expect a response in 2 to 2.5 weeks later whether I was successful or not. Anyway, 3.5 weeks late no response and I sent an email to recruiter about the status. At this stage I’m getting a bit annoyed about this.. what should I do? Send another (more frank) email about when to expect a response? Should I email just the recruiter or those who interviewed me?

Thanks :)