Do you remember this thing? It was introduced as an "anti-mascot" in 1984. Crazy Crab lasted only one season. It was the subject of much derision and abuse from players and fans alike. Here is a little article about it on the Giants website.
Here's one of the commercials from 1984:
I guess the Giants gave away some bobbleheads (or bobblecarapaces in this case) last year:
Here is Crazy Crab making its "triumphant" return in 2008: