I think the boundary is well-defined (tech companies are not the first companies to hire people): don't drink alcohol at work, don't smoke weed at work (even if it is legal), and don't come to work drunk or high.

If it is a social event outside the work place/hours, you can drink but don't get fucked up and vomit in a pint glass. If weed is legal, you can go outside and smoke like tobacco but, again, don't get fucked up and try to hump a pot plant or something.

Simple.