Flea is a derogatory casino nickname for a player who bets small but expects big perks, such as free drinks, meals and rooms (RFB) or comp points far beyond what their play has earned. Fleas tend to be loud about it, pressing dealers, hosts and pit staff for freebies and complaining when they are refused.
In land-based casinos, comps are based on rated play and staff discretion. Big and regular players earn them, and hosts sometimes reward a player who is having a rough night. Asking repeatedly does not change the formula; it only slows the game and irritates other players and staff. Because the word is an insult, it is best not used within earshot of anyone.
Rules beat negotiation
Online, the closest equivalent is a player whose activity revolves around promotions. Transparent loyalty rules, with points tied to real stakes, remove the need to negotiate and keep reward costs predictable.