Can I use my US passport card to get served in a drinking establishment? I do not have a driver's license and don't like carrying my passport around with me.
This generally varies by locality. Most places, to my knowledge, simply have laws limiting the age of persons wishing to drink. How that age is determined may be left wildly open to interpretation in some places, while other jurisdictions may require specific forms of identification.
In most places, any government issued ID will suffice from a legal standpoint, although it's often up to the particular security guard/bouncer whether he wishes to accept your ID.
I was with a Mexican friend once in the US, who was denied entry into a bar because the bouncer could not read the birthday on her Mexican-issued ID. If she had been carrying her passport, I expect she would have been allowed in.
I would be somewhat surprised if there are any laws that require that a passport (card) be considered a valid proof of age, but I would be even more surprised if there are any places that prohibit it. This means it's mostly going to be left up to the local security guards to make a judgment call.
In most places, I imagine it would be accepted.
The US Passport Card is a valid "REAL ID" form of identification, and thus is recognized as valid ID by all US Federal and State Government departments, in exactly the same way that a Passport is.
So officially, yes, you can use your Passport Card as valid ID in a bar within the US. There is obviously always the risk that the person checking ID's will not be familiar with a Passport Card, however they should have access to a guide that includes details on all valid ID, and the Passport Card should be included.
Outside of the US it is likely to be a bit hit-or-miss, as very few countries have any form of passport "card". Given that it does look like official US ID, it's likely it would work in many locations, but would not be as reliable as a real passport.