I would look at the Battle of Peleliu for some answers. The campaign was fought in order to secure MacArthur's flank for the Philippine invasion. Peleliu arguably became the worst battle the Marines fought in the Pacific campaign with over 11,000 American casualties. Sadly, many critics pointed to the fact that securing the island was unnecessary, meaning that MacArthur sent thousands of marines to die for nothing.

Additionally, sources vary on the character of MacArthur. Some personal staff enjoyed serving with MacArthur. Others, including staff (like Ike) and subordinates, argued that MacArthur was a unsympathetic general who enjoyed theatrics but took poor care in looking after his troops. Furthermore, its is widely regarded that MacArthur was the biggest prima donna in the war, known for his arrogant confidence.

Your father may also have disliked MacArthur for his leadership style in battle. First, MacArthur failed to act or prepare for an imminent Japanese attack on the Phillippines after the attack on Pearl Harbor (he had approximately 24 hours to prepare). Second, he fled from the Phillippines before the Japanese victory (I would assume thats another "no no" for your father). Third, MacArthur had a tendency to direct his troops from the safety of rear line headquarters. For instance, in the first few months of the Korean War, MacArthur stayed and commanded his troops from the comfort of Japan across the sea.

Comparing MacArthur to other leaders in the Pacific during WWII may also shed some light on your father's disgust for him. Look at Simon Bolivar Buckner. He was a three star general famous for his lead from the front mentality. Interestingly enough, General Bolivar was killed by artillery on a reconnaissance mission during the Battle of Okinawa. One can also look at the big personalities that dominated the Marines during the war. Chesty Puller, Merritt Edson, Ray Robinson, and John Archer Lejeune are a few notable marines known for their leadership capability.

I cannot speak for your dad, but I can assume that some of these reasons may have contributed to his his dislike of MacArthur.

As commander of the U.S. Army Forces in the Far East and then the Southwest Pacific Area MacArthur had relatively little command or influence over USMC units. His forces consisted primarily of US Army and Australian units. Three particular events do however spring to mind :

In late February 1942 as the Japanese besieged US and Filipino forces in Bataan and Corregidor, President Roosevelt order MacArthur to personally leave the Philippines and re-establish a headquarters in Australia. This necessarily meant leaving thousands of troops at the mercy of the Japanese. Among them were the 4th Marine Regiment and a number of supporting units.

In December 1943 as part of operations intended to eliminate or isolate the major Japanese base at Rabaul, Operation Cartwheel, the 1st Marine Division was landed at Cape Gloucester. Even when compared to the terrain on New Guinea and Guadalcanal the jungle here was virtually impenetrable and the marines made only limited progress. Eventually the campaign on New Britain (the large island with Rabaul at it's eastern end) was essentially abandoned in favor of and advance along the New Guinea coast. The operation was largely a waste and no practical use was made of the land gained.

Finally. in September 1944 the 1st Marine Division (again!) landed on the island of Peleliu. MacArthur had insisted that the island be taken as part of the advance into the Philippines. However numerous others, particularly the Navy chiefs, had protested against this arguing that both the invasion of Peleliu and the Philippines operation in general were unnecessary. The fighting on Peleliu was some of the most savage in the war and securing the island took 73 days.The 1st Marines alone took over 30% casualties. While fighting was still raging on Peleliu, MacArthur was getting most of the press attention by wading ashore at Leyte on 20th October 1944. It is likely this battle that your grandfather is remembering.

Hope that helps. Incidentally the landing at Peleliu was re-created in the BHO mini-series The Pacific in episode five.

There is a lot of institutional resentment for MacArthur among marines for his actions in the Korean War as well, in particular his placing the First Marine Division under the command of Ned Arnold for the amphibious assault at Inchon, and the series of dubious orders given to it afterwards that led to the Marines being surrounded at the Chosen Reservoir.