Over the top
To an excessive degree; beyond reasonable or acceptable limits.
In the First World War the phrase was used by the British to describe the infantry emerging from the safety of their trenches to attack the enemy across open ground. An early example of that in print is from a 1916 edition of War Illustrated:
"Some fellows asked our captain when we were going over the top."
More recently, with allusion back to the WWI usage, the phrase has come to describe excessive or foolhardy actions. This figurative use originated not long after the war and the earliest record of it that I've found is in Lincoln Steffens' Letters, 1935:
"I had come to regard the New Capitalism as an experiment till, in 1929, the whole thing went over the top and slid down to an utter collapse."
Since the 1980s, in the UK at least, the phrase is often shortened to OTT.
O. T. T. was the adult version of the anarchic children's TV show Tiswas. It was broadcast by the UK television network Central Television in 1982.
Barr and York's Official Sloane Ranger Handbook, 1982, included a definition of OTT:
"OTT, over the top - outrageous. Usually 'absolutely' or 'totally OTT'."