lose one's cool
Not staying cool and in control. The opposite is to keep one's cool.
Don't lose your cool, man!
One will fail if one lose one's cool.
One will fail if one lose one's cool.
losing one's cool
To lose one's composure. Most people lose their cool when prompted by a negative impetus, like sexual rejection or poor brunch service.
"Losing one's cool is the sexual equivilent of an angry, limp penis."