Ai Farang is crass and maybe intent as derogatory, but I wouldn't say offensive, there is nothing to be offended about, but to have such shop talk coming out of a minister's mouth however reflects more on the speaker
it all depends on the way it's being said
Farang, Dam (Black), or just simple 'You' or 'Oun' (Fattie) can be used in place of pronouns by Thais trying to communicate, endearingly or as snide