The act of holding in faecal matter beyond it's natural release point, to the point where it is bubbling to get out. At this point the dirty payload is then released onto the waiting stomach of a loved one in an act of tarmacking (see 'tarmacking')
Lee has had one simmering on his hob for a few hours now while Laura is waiting by the fire for a good tarmacking.
An attitude combining simmering anger on the verge of explosion with the subsequent inevitable progression of attitude into verbal explosion- hence the rant.
To be boiling beneath the surface with only the slightest skin of resistance between restraint and going postal.
After being dumped by his girlfriend for a state trooper, Todd was the picture of simmerant when he was pulled over on the way home by the very same trooper.
