Originally a word for someone who is a drunkard, over-fond of ale, of tossing the pot of ale back.
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.
"But when I came unto my beds,
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.