The act of bidding something you're not going to pay for, typically used on eBay and other online auctions. Shitbids are often a ridiculously high price much, much higher than the value of the actual item being sold. A shitbidder usually targets the person selling the item, often with the intention of making the seller lose money due to a personal grudge.
I posted something on eBay and somebody shitbidded it up to $5000. Now I have to pay to relist it again because he didn't pay.