There are some behaviors that are nearly universal amongst the bilingual at least in English* Many of them are annoying.
But they appear to be organic, and will probably be a part of the learning process as long as English is the easiest common language.
This question occurs with bizarre predictability, in exactly the same form and always in English.
It's meaningless. Nobody understands anything completely. And why English? That's an ignorant way to treat somebody who's trying to listen to another language.
It's mysterious behavior and ubiquitous. There's one in every crowd.
Almost as annoying and a lot more prevalent is the eagerness of the bilingual to help, interrupting a conversation to offer translation.
If two people are trying to learn each others' language and are having minor difficulty, that is exactly what they need.
One would think that the bilingual would at least offer a minor delay before popping in with annoying help that is no help at all. But that's not how it works. It never stops. To convince even one person, you must beg please do not translate for me. It probably won't work. And there are always more of them.
The bilingual, when they bother at all, will probably do so in a patronizing manner.
Sometimes, only trying to help, they will talk so slowly that it's hard to even pay attention. The rhythm is unnatural and the practice is irritating, which adds another element of distraction.
Sometimes the bilingual will begin speaking in his language and it may seem like he's giving you a chance.
Usually, he's just trying to "lose you" to push you beyond your ability. You want to speak in our language? Here it is more than you wanted. He's trying subconsciously, not intentionally to dispense with your efforts and get back to speaking English.
I had somebody teach me how to say in Romanian "There's no need to test me." He was one of the worst offenders and is still a friend of mine. But I never did convince him.
If you can display an unusual ability with a language most people don't bother to learn, there are going to be people who will want to show your skill to their friends. This is flattering, but again the rhythm of conversation is unnatural, often too fast, and not necessarily logical in a normal conversational sense. Now, with the pressure to be impressive, you're supposed to know how to respond.
The bilingual are an enormous pain in the ass, and nearly useless to a student of their language.
*These behaviors are likely present in all encounters where comprehension is non-symmetrical.
English may be a special case, though, since it is the principal global tongue.