check out SIRI friday, 30k calls traded, $2 JAN14. looking back on the chart there was also a 70K block day back in march on the same contract when the underlying was last over $2.
i'm sure there was no simply hitting the bid/ask, or placing a limit order and seeing what happens. once an order is big enough to move the market if placed, it would be in the buyers/sellers best interest to work with the market maker directly, rather than though the market first, no? splitting the spread, both working their end of the trade for a benefit. are large block option trades like this perhaps trades between option MMs, and HFTs playing MM in the stock? giving each some insurance, some inventory, and some cushion to work with day-to-day.
otherwise, an arb opportunity greater than what the maket maker(s) controls would be open to the market all the time through greater volume (duh, i think this exists already, by design), but why let your order create an arb opp for someone else to take advantage of? what if that 30k contracts was placed as a market order, blowing though the option MMs book, would it only get filled once the market absorbed it, at whatever price that came to? why would the buyer/seller do this? i'd think they would feel out the market, and see what it could absorb first.
