Earliest example of this known is in 16th century Elizabethan English,
Shakespeare's play "Twelfth Night", has the word in the closing part of the play, in Feste's song.
Nice to see it's still used, even if the meaning could be slightly different.
With hey, ho, the wind and the rain,
With toss-pots still had drunken heads,
For the rain it raineth every day."
That Kevin is an effin tosspot, pissed out of his head again.
A toss-pot is a drunkard, a toper; a would-be alcoholic still managing to function in society.
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