11) Don't just sit there and introduce yourself!
12) Don't just sit around and eat!
Is it right that those two sentences eventually convey Don't sit and also don't introduce in #11 and "don't sit and also don't eat" in #12?
If there were commas in front of "and" as follows, then could they change the meanings and the sentences eventually say that you have to introduce, not sitting there in #21, and you have to eat, not sitting around in #22?
21) **Don't just sit there, and introduce yourself!
22) Don't just sit around, and eat!
Then if the two commas should be left out, you can't still understand them just as there were commas?