"Hello, Alexis, welcome to ELU." In the sentence I just typed, I am addressing you (Alexis) directly. That is referred to as direct address, which is offset by commas when in the middle of a sentence. (See rules in link below.)
https://www.btb.termiumplus.gc.ca/tpv2guides/guides/wrtps/index-eng.html?lang=eng&lettr=indx_catlog_c&page=9J8lRcRhJ-78.html
So, the placement of commas in the first sentence...
Hey, pretty lady, you seem like fun.
...before and after the direct address ("pretty lady") is correct.
Always use a comma when directly addressing someone/something,
regardless of whether the direct address is at the beginning or end of
the sentence. If the direct address is in the middle of a sentence,
use a pair of commas to set off the direct address.
http://www.grammarerrors.com/punctuation/commas-in-direct-address/
That being said, leaving commas out of greetings (with direct addresses in them) seems to be a common error that is, perhaps, becoming more prevalent.
Example sentences:
Hey, honey, pass the honey.
This chair goes over there, sweetie.
Would you like a chocolate bar, little one?
“Hey, buddy, pass the chicken.”
“I’m distracting you, little turd blossom.”
“Hey, dude, check out that chick.”
“Hand over that phone, jerk!”
See #7: https://dianetibert.com/2015/03/09/when-to-capitalize-names-that-are-not-names/.
Some examples aren't so endearing. See more examples in the link below. Have a nice day.
https://www.thoughtco.com/vocative-grammar-1692598
