have a cow

to completely and utterly flip the f-ck out.
mary really had a cow when she came home from work early caught me sticking it to her twin sister indab-tt over the kitchen counter. typical woman, always overreacting.
(have a cow)
a frequent utterance of bart simpson, “don’t have a cow” dismisses the other person’s feelings as overreactive to the situation. the person who expresses anger, shock, disgust, or any of several other negative feelings towards an action or person is seen as having a cow. the person who induces bovine delivery, either through doing it or telling of the activity, often tries to minimize the activity as something not so bad. saying don’t have a cow minimizes both the activity itself -and- the person’s feelings who is having the cow.
jimmy joe had a cow when he learned that his best friend, john jay, had bought a term paper online and p-ssed it off as his own writing.

billy ray laughed at jimmy joe’s shock that he could do such a thing. he sneered, “don’t have a cow, man! professors never read those papers anyway.”
as in when a person will be extremely upset, angry, or suprised about something
bob: hey, did you hear about how fred’s house got bulldozed over while he was on vacation?

joe: yeah, he’s going to have a cow when he finds out!
instead of saying. keep your kinckers on really. just a lil’ bit more hip and modern. yeah.
‘i f—— hate you man’
‘wooh. don’t have a cow man.’
the “country folk” version of “have a cow”:

your dad owns a dairy farm, so when mom and pop go out for dinner, you go out into the barn with a can of aerosol whip cream and spray it on your naked b-n-r so one of the calves will suck you off.
clyde: hey, enos, are you going to the prom?

enos: no, all the chicks i asked turned me down. i think i’ll just kill myself!

clyde: come on man, it’s not that bad — have a cow!