If I'm in a lecture on linguistics acquisition, and you say, "Do you know what 'sibbing' is?" while pointedly playing with confetti, it's going to take me a while to get it. It's not that I don't get it eventually, or that the context isn't clear; it's that I've been trained over years of experience to react to that sort of situation by wondering what I missed, and searching - consciously - through a list of possibilities that are already in my lexicon - did you say sibling? Fibbing? Sipping? Sitting? Flipping? Fitting? Flitting? Holy crap, even now I'm confused. Especially if I'm not looking at you, and thus there's a delay while I figure out whether you're talking to me, or the person just behind me. If you're gonna pull a surprise-ish demonstration like that, don't pull it on the deaf guy when he's busy watching the interpreter.

And for the love of god, if you're talking about minimal-pair phonemes, *don't* say "TA" and "DA". Specify the difference explicitly: the first is voiceless and the second is voiced. I may be a native speaker of English, but I still can't differentiate those in isolation. Not in an environment with background noise. And from some of the reactions I saw in class, I think the hearing students felt the same.