To "go apeshit" is to act with regards to or react to a situation or environment in a particularly emotional or expressive manner. Example of usage: My parents went apeshit when they heard I had three "F's" on my report card. The phrase "going apeshit" is a less-polite synonym for "flying off the handle", another idiom connoting a dramatic and angry reaction. In psychology and common terminology, emotion is the language of a persons internal state of being, normally based in or tied to their internal (physical) and external (social) sensory feeling. ... The letter F is the sixth letter in the Latin alphabet. ...

References

• Urban Dictionary definition