I’ve had a container (plastic) of white vinegar in the trunk of my car for a few months. Its been pretty hot lately… Is it safe to cook with. Can it spoil?
It should be fine. White vinegar is just a 5% solution of acetic acid in water. Barring evaporation, nothing’s going to happen to it, or grow in it. Even diluted 1:1 with water, white vinegar effectively prevents the growth of bacteria in canned vegetables, such as pickles. You might have a bit of leaching of plasticizers from the plastic container, but that happens whether it’s kept in the trunk or not, and the manufactures do use food grade plastics
Pure white unflavored vinegar (dilute acetic acid) probably wouldn’t go bad, as there are few other organic molecules in it which would decay from heat or bacterial action to give it bad flavors. However, the heat could tend to promote reactivity in the plastic (it does happen, plastic’s not completely inert) and give bad flavors that way.
Taste it and let us know! 
Shake well!
Actually… do not shake well. If there have been reactions with the lpastic (doubtful), the products would certainly fully end up in the vinegar upon shaking. I would slowly decant it, and use it.