It depends. A little levity is fine. Doing so at expense of clear/readable code is not. If I have to debug some code with 'comedy' variable names I will get quite grumpy about it, for all the reasons I'd get grumpy if you just used single letters all the way through.
But in comments (as long as you _also_ include the comments that you _need_) it's fine and great. In error/diag messages too (again, provided you're actually producing _useful_ output as well).
<code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>