I’m sure there have been many variants on this topic before - the one about ordering milk in a bar was a good one. What brought it to mind this time is a coworker who sips drinks out of a cup with a straw all day long. Normally I wouldn’t give it a second thought if it was at a fast food restaurant or the movies or something. But our company just switched to paper straws and this guy had such a fit I realized that pretty much any time I look at him he’s sucking on that straw. Had he not been about to go ballistic, I would have said “you’re a 52 year old man; learn how to drink from a big boy cup”.
Another example is a local radio host who insists ice cream cones are for children; adults should be eating out of a bowl only.
Finally, same office - different co-worker- has very strong opinions about adults eating those Lunchable snack packs (essentially cheese, meat and crackers ostensibly for kids to bring to school).
Are there any behaviors that you find somewhat childish when you see an adult exhibiting them?