Impromptu requests for your time and attention come up all the time. Here’s how to handle them professionally, rather than just swatting them away.
“Sorry, I’d help you if I could, but I’m tied up doing this other thing for someone else.” It’s a common way to beg off new requests, but it may have the unintended consequence of slighting the asker. There’s no doubt you have legitimate reasons for not being available. But there’s still the risk that you’ll make your boss or coworker feel like a low priority when you pass the buck in the process of telling them “no” or “not right now.”