pink gooshie thing

My son this morning said he wanted some playdoe, i told him we didnt have any. He became a broken record.

then he said "find me a pink gooshie thing" in his 'argumentative voice.'

he just kept going on and on with insisting me helping him find this pink gooshie thing.

I told him we dont have a pink gooshie thing, and he insisted that i go to the store and buy him this.

this went on and on with me just staying calm and saying we dont have a pink gooshie thing.

finally i couldnt take it, so i told him i was goinng on the bedroom to get away from the conversation.

he of course followed me, so i closed the door on him and he tried to break down the door to come in.

any suggestions, this is an on going issue and it is getting worse.