Silly, it's clearly a crushing tankard.
These mundane tankards (or steins) look like their normal sturdy counterparts but are made of much thinner aluminum than their appearance would otherwise suggest. These tankards are used by drunken hooligans to impress their equally drunken drinking buddies. By crushing the tankard or stein against your forehead, you take one point of damage and gain a +1 circumstance bonus to impress any drunken ally within 10-feet of you who witnesses you crushing the tankard or stein against your forehead. Non-drunks are usually unaffected, but a few (5%) are actually put off by such juvenile behavior. You can throw a crushing tankard (or stein) as a improvised weapon but your target only takes one point of damage and the tankard breaks and becomes unusable.
And if you ever need stats for a mob of drunken hooligans, I have it here: http://www.giantitp.com/forums/showt...1#post14483061