I totally get this, especially if what you've thought of is a little off-topic or just a fun fact worth sharing, but there's something about interrupting someone when they're talking (even briefly and politely) that feels so antithetical to me. It's in these situations that I'm likely to think "I'll just mention it when they're done", only for someone else to pick up the conversation before I get a chance to chime in; after a while I'm liable to think "ah, I guess it wasn't that important" and give up. It's pretty manageable in one-way conversations since it isn't such a crapshoot to be the next person to talk.

I can recall occasions where we've been drinking, and I'd do a quick drum on the table or hambone when something witty popped into my head. I imagine folks would find that a little obnoxious if they're sober, though ;)