The Dallas Mavericks just can't seem to peel themselves off the doormat ... even Southwest Airlines is now taking popshots at them!!
The plane co. dissed the Mavs in an Instagram post on Thursday ... making fun of the NBA team's controversial Luka Doncic trade while defending its new checked bag policy.
In an effort to try to soften the blow of telling their customers they're now charging some of them for checked luggage .