«Unwelcomed Visitor» by William Morrison

Unwelcomed Visitor written by William Morrison - Xhanph was the fully accredited ambassador from Gfun, and Earth's first visitor from outer space. History and the amenities called for a tremendous reception. But earth people are funny people…
All the way over, all through the loneliness of the long trip, he had consoled himself with the thought of the reception he would get. How they would crowd around him, how they would gape and cheer! All the most prominent and most important Earthlings would rush to see him, to touch their own appendages to his tentacles, to receive his report of interplanetary good will. His arrival would certainly be the most celebrated occasion in all the history of Earth….
He was coming in for a landing, and it was no time for day-dreaming. He brought the ship down slowly, in the middle of a large square, as carefully as if he were settling down among his own people. He gave them a chance to get out from under him before making contact with the ground. When the ship finally rested firmly on the strange planet, he gave a sigh of relief, and for a few long seconds sat there motionless. And then he began to move toward the door.
The increased gravity did not affect him as badly as he had thought it would. For the dense atmosphere, with its high oxygen content, he had of course been prepared. He injected another dose of respiratory enzyme into his bloodstream just to make sure, and then swung open the door. The inrush of air caused only a momentary dizziness.
Then he climbed over the side and stared about in surprise.
No one was paying any attention to him.
Their indifference was so enormous that it struck him like a blow. Individuals of both sexes—he could easily distinguish them by the difference in their clothing—were going about their own business as if he simply were not there.