【fly off the handle】 —(coll.) get into a rage; lose one’s temper:

• When we are under stress, we are more likely to 【fly off the handle】 .

【go off the handle】 —(coll.)

1. = 【fly off the handle】 :

• Jimmy went off the handle at once; and Nicol kept patting him on the back.

2. die:

• My old gentleman means to be Mayor before he goes off the handle.

Note: Neither expression is antonymous in meaning to the phrase get a handle on something—understand or be able to master smth. fully:

• This book should prove useful for anyone who wants to get a handle on this complex subject.