Yes, the most annoying thing is they require previous experience for low skilled jobs.. A more annoying thing is when an agency calls you and says that the job you've applied for is difficult, which means they don't believe you can do that job.
Or some employers like I've sent off my CV as they were in need of an interpreter and they clearly mentioned YOU DO NOT NEED PREVIOUS EXPERIENCE and that they will take on students. After I sent my CV and got no response, after few days saw the same ad from the same company saying that now YOU DO NEED PREVIOUS EXPERIENCE and diploma in interpreting... I've wasted my time writing cover letter and tailoring my CV to find out how immature the employer was..
Oh and employers who expect you to have good English language skills whereas they clearly make grammar mistakes in their job ads. Especially one agency which constantly makes grammar mistakes in their job ads..