on the blob

(menstruating): Apparently a reference to the blobbing (i.e. dripping) of menstrual blood, likely following the model of on the rag.

on the blob

1. (British, slang, vulgar) Menstruating; on one's period.

   Synonym: on the rag

   • 1993 April 19, Sean McAfee, “The Great a.t. IRC Party, part III”, in alt.tasteless‎^[1] (Usenet), message-ID <1993Apr19.224852.14466@mtu.edu>:

     <julian> I have no problems fucking wimin on the blob. But some of them do

   • 1997 July 3, Nicholas Lezard, “Paperbacks”, in The Guardian, page A14:

     Sweet's heroines are – well, unskinny; they eat lard, drink, smoke, ponce off the state, have huge dumps and go on the blob at inconvenient times.

   • 2012, Damon Beesley, Iain Morris, The Inbetweeners: The Complete Scripts with Added Extras, Random House, page 285:

     Katie Can you stop staring at my tits please? […]
     Jay She must be on the blob.

   • 2015 February 13, Caitlin Moran, “Celebrity Watch”, in The Times:

     Personally CW can think of no tampon in the world it would trust while wearing a white dress, on the blob, at a glamorous media event.

2. (UK, slang, obsolete) Of begging etc.: performed by speaking to people, not by writing letters.
   • 1851, Henry Mayhew, London Labour and the London Poor, published 1861:

     With this excusable class, however, I have not now to do. Of professional beggars there are two kinds—those who ‘do it on the blob’ (by word of mouth), and those who do it by ‘screeving,’ that is, by petitions and letters, setting forth imaginary cases of distress.