Most wildlife will disappear or distance themselves from a potential threat, such as people getting too close for comfort. Depending on the situation, fear is surpassed by some animals and they become oblivious to what is going on around them. I have seen two robins having a scrap outside a cafe in the street - they just seem to be lost in their own little world and unaware that they risk getting trodden on by morning commuters. A sparrowhawk can be so engrossed with its prey that it doesn’t notice approaching people as a threat. This type of behaviour is mostly likely to arise as a result of food, rival males or defending territories.
These two willets were fighting in the surf on Fort Myers Beach, Florida. Despite people playing in the water and others walking by along the beach, they continued to fight. After several minutes, the fight was over and the birds went their separate ways.
Nothing like a bit of free entertainment whilst on the beach.