An old English double-noun which, because of the use of the word, toss and its own synonymous resonance with masturbation and wank, does not mean "a wanker".
A toss-pot is a drunkard, a toper; a would-be alcoholic still managing to function in society.
Oh, for fuck's sake, you haven't left the cellar key with that old toss-pot?
You really are a silly old toss-pot, aren't you? I was, I guess, somewhat taken aback when you threw up all over the Bulgarian Ambassador, but I do so love you very much, Poppet. x