:::::Try actually reading your Google hits instead of just counting them.  Of the 114 *unique* hits for "aluminum underwear", 79 have nothing to do with shoplifting, 28 directly concern the Colorado law, and only seven generally concern shoplifting, not specifically in reference to the Colorado law.  Of the 35 unique hits for "aluminum underpants", 18 have nothing to do with shoplifting, 17 reference the Colorado law, and zero reference shoplifting in general.  It is obvious from these Google results that the use of the phrase in either form did gain some popularity surrounding the passage of the Colorado law, but disappeared shortly thereafter and did not fall into the general vernacular.  Either form is therefore not ubiquitous and is inappropriate for this section title.