When a situation becomes violent, dangerous or risky - for example, walking into a
pub or bar and the atmosphere is already hostile, and all it
will take is one wrong word, one spilled drink or a
single push or shove before a fight breaks out.
Can also be used by a single person when they've been pushed to breaking point as a warning to others.
(In a
pub or bar) "Let's get out of here, it's going to get pristine in a minute"
(Person in a bad
mood) "I've been up since five this morning, I've had a really bad
day and it's going to get pristine in a minute..."