I often ask patients to "squiggle over a little bit on the stretcher," so that their arm will be resting comfortably permitting a relaxed blood pressure measurement, rather than having to hold it up tensely in the air. It has the advantage of being understandable but a little bit silly, usually elicits a smile and eases tension...

granted it's not [I must acknowledge, upon re-reading the original post of this thread] a particularly powerful word