A bar or club that only lets in regulars. Only a few bars are true paradoxes. Others instead only restricts their audience to regulars on certain weekdays, or between certain times - or a combination of both.
Bouncer: "Sorry, we only let in regulars today. You're not going in."
Non-regular A: "What? How can you be a regular without being let in regularly? This bar is a paradox"
Non-regular B: "Yeah, fucking Paradox Bar"
C: "Wanna go down to the Havana Club?"
D: "Nah, we'll never get in - it's a Paradox Bar"