Exactly, most westerners with English as a first language can adapt, which takes time if you only fly into the US a few times a year.
Hearing some ATCer get angry at a foreign carrier with a guy who clearly has english as a second or third language as previously said is pointless. He was trained to an ICAO English proficiency what else can you expect.
Use slang and style with the locals and carriers who can/have adapted and standard ICAO with those that are expecting just that.