Ask HN: How do I backout of an accepted offer

Legally.

But there might be another question. To what degree do you consider that you gave your word? And how much is your word worth to you? If you're a "my word is good" kind of person, then "legally" isn't the only consideration. You might see if you can get the company (or your friend) to release you from your acceptance, to whatever degree you feel is needed.

"When I was interviewing for the job with you, I was also interviewing with other companies. Your offer came in first and the job sounded interesting and the pay was good so I accepted. However, since then one of the other companies I interviewed with has given me an offer for a more interesting/better paying/shorter commute/etc. job and so I've decided to accept that offer. I hope this doesn't negatively impact you and that you can quickly find someone else."

Or something like that. Tells them the honest reason why, doesn't burn your bridge too badly.

Almost the same way as you said in this post. Don't mention the panic, do mention that the other offer is personally very interesting to you.

Do this after you have accepted and confirmed the second offer. The earlier you do this the better.

There is of course value in keeping your word once you have accepted something - but for how long would you work at a less interesting position for just that? A few months, a year, 3-5 years? If under a few years, then you aren't actually helping them by accepting and "keeping your word".

(If it's just about the money and they offer, it's a different dilemma).