To be 'lightly toasted' is to be stoned due to the use of marijuana.
This phrase was apparently popular in some circles in the early 1990's... according to this philosophy professor I had this one time.
Advantages of the phrase 'lightly toasted' over other more common terms:
1 - It is basically a thinly veiled version of the more popular adjective 'baked,' and yet it is somehow ambiguous enough to be used in virtually any environment without anyone being the wiser.
2 - It invokes images of lightly toasted food, which is always pleasurable to think about and even better - to consume when you yourself are 'lightly toasted.'
3 - You can insert the phrase into a sentence about food and in so doing tip off only those cool enough to understand.
"My kid's chorus performance is going to bore me to tears. I'd better get lightly toasted before I go."
(the stealthy approach):
"Hey guys, I could go for some *lightly toasted* Popped Tarts right now... (wink wink) What about you guys?"
(or it can even serve as sexual innuendo):
"Hey baby, let's get lightly toasted then you can butter my bacon while I scramble your eggs."
The possibilities are endless. So, go out there and spread the good word my friends. We won't stop until the whole world is golden brown.