What is the ruling on eating and drinking with a person who prays at times and abandons prayer at other times, and creates a problem whenever asked about that?

Abandoning prayer is one of the gravest sins. The one who abandons it must be advised and prohibited from their action. If they do not desist except through boycotting, then they should be boycotted in food and drink. However, if there is no overriding benefit in boycotting them, then whatever serves the best interest should be done with them.