Replying to Complaint Letter

I was recently given an assignment for my business communications course, to write a complaint letter. Easy enough right, well except i cant think of anything and its due tomorrow. So I'm coming to you guys, tell me about something you'd like to complain to a company about and ill get a topic for my paper! or if any of you guys have written one before let me know, I would really appreciate any help, Thanks guys. KARMA for anyone who helps