Guys, What would cause a man to disrespect one woman's boundaries but respect the boundaries of a different woman?

Asking in regards to recent behavior I observed. Noticed a guy treating his ex-girlfriend (very smart, well-educated, accomplished, attractive woman in early 30s) with utmost kindness and respect throughout their relationship, even after they broke up (he was the one who initiated the breakup). He always respected the boundaries that she communicated to him and never challenged them.

However, observed the same guy acting sleazy numerous times towards another woman of very similar background, appearance, and personality - only exception is less degrees and less accomplished than the ex-girlfriend, but still holds impressive credentials in her own right. Also late 20s instead of early 30s. This woman is married and pregnant. He has repeatedly disrespected her boundaries and made lewd, inappropriate comments towards her.

What would cause this discrepancy in behavior? Since he is broken up with the first woman, I assume he does not want or need anything from her that would warrant treating her with more respect. Given the second woman is married and pregnant, not sure what he would want from her either.

Guys, What would cause a man to disrespect one woman's boundaries but respect the boundaries of a different woman?
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