To make your cocktail party more participatory, have your guests grill their own skewers. A hibachi is even more user-friendly than a grill, since the ends of the skewers hang out over the edge, eliminating the need for tongs. If you're cooking everything yourself, it's easiest to use a large grill or a broiler (see cooks' note, below) and serve the skewers in batches.
• Skewers can be threaded up to 2 hours ahead and chilled separately, covered with plastic wrap. • To broil skewers, preheat broiler and oil rack of a broiler pan. Put 1 batch of skewers in 1 layer on rack and broil 2 to 3 inches from heat, turning over once, until beef is medium-rare, about 3 minutes total; chicken is just cooked through, about 3 minutes; shrimp is just cooked through, about 2 minutes; and mushrooms are tender, about 4 minutes.
