Figuratively: Someone whose shitty driving will soon cause them to be found dead on the road, just as actual opossums are often found.
(You are on a 3 lane freeway in the Summer. A person driving 45 mph, goes from the right lane to the middle lane, directly in front of you, without using their turn signal)
YOU: (Yelling sarcastically out the window as you pass) Thanks for the turn signal Opossum!
If I can't tell if a person is a man or a woman, I call it a Glabbit.
When you move beyond the have a cow
stage, and you actually find some chick (or guy) who will suck you off. You spray some aerosol whip cream on your rock hard cock to give your cocksucker some pleasure while she (or he) pleasures you. That spray whipped cream cums in lots of flavors now!
Miss N. Cox said she would suck me off (but I had to pay her). She said she would only do it if I covered my cock with Strawberry Whipped Cream every couple of minutes. What a dream whip! Not ALL of the cream came out of a can!!! She swallowed every ounce of my cum without hesitation.
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 boner 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!