a. 'you'd rather not' is more like 'i don't think you should do it' while 'you don't want to' implies more of a 'i don't think you'd like the consequences (results) if you do that certain action'. b. in that specific sentence it just means there's no chance of you going to this place, in this case mcdonald's, not drunk, which is sober. 'mcdonald's sober' is not a phrase. it's just 'you're not going to go sober' and this place you 're not going to go sober is 'mcdonald's'. Hope it made sense :)