When a friend has run out of luck with a job, relationship or just life in general, they are floating along like toast on the water. Their situation, the toast, is now becoming soggy and tearing apart by the waves. Now they are waiting to sink to the bottom and become fish bait. Their only hope is to be picked up by a sea gull to have the misery swiftly ended.
The person loves themselves that much, they are so up themselves that if they had a round of toast they would definitely spread themselves on it. They are loving themselves sick.
'look at her over there, she is definitely having herself on toast'