In sports, the greasy butter one feels on the sweatband of a helmet that is used by multiple people. It's a positive indicator that the helmet has never been cleaned. Helmet butter is ubiquitouslying noticed when picking up a sports helmet, is very greasy to the touch, and usually makes one grimace until they can sanitize their hand. Helmet butter is not USDA approved, even though it's viscosity is measured in calories. The FDA has started clinical trials as to helmet butter's efficient properties for being a gag-reflex inducer, and is likely to get approval.
Coachs handing out helmets to participants often say, "yuck, my finger is covered in helmet butter!"
by Dr Drew, PhD October 13, 2016