You might think that throwing some good jokes into your cover letter will make you stand out from the rest. Sure it will. In fact, your letter might be passed around someone's break room so everyone can laugh at how funny you are. There's a whole raft of reasons why joking around in a cover letter isn't a good idea. Basically, if you want to be seriously considered for a job, you need to act like a professional -- which means no jokes. Plus, you have no idea who will be reading your cover letter. What if it's the office crank, who hates jokes? If you make it to the in-person interview stage, it may be possible to turn on your inner comedian to break the ice (assuming you've evaluated your interviewer's personality first), but even then, it's safest to be serious [source: Smart Biz]. Unveil the comedy routine once you're actually on the payroll.