Some User Experience Maxims

The user experience can only be positive if there are no negative factors ruining it.

Here are some things to consider:

Don't annoy users by locking them out, instead try to support all popular devices and browsers, and make the site or web-app accessible.
Don't annoy users by wasting their time, instead make it possible to reach the respective objective fast and ensure high performance.
Don't annoy users by leaving them confused, instead make everything clear and obvious.
Don't annoy users with unreliable code, instead make sure that the web-app is robust.
Don't annoy users with animated ads and ads that show what they had already looked at, instead ensure that ads aren't distracting or annoying.
Don't annoy users with low quality, instead make sure that the web-app yields results of high quality. (For example when you provide public transportation connections make sure they're fast, or if you provide music/image files make sure they're not compressed too much.)
Don't annoy users by playing sound without the user's consent.
Don't annoy users by suggesting a smartphone app while they are on your site and the web-app is a fine option.
Don't annoy users with (too many) push notifications.
Don't annoy users by lazy-loading eg images eg on scroll-into-view, because that keeps them waiting.
Don't annoy users by having all the main content (of the whole website or of a long page) positioned on one side, because the twisted posture causes strain. Instead center the main content.
Don't annoy users by cluttering the screen with overlays etc. Some links: cluttered mobile screens 1, cluttered mobile screens 2.
Don't annoy users by popping up stuff on hover. People might need to move the pointer for other reasons, without the intention of popping up eg the menu. If the things that appear accidentally on hover obscure other important page items then that's a problem.
Make sure that there's nothing else that might annoy the user.
Users want options, but making choices should be quick and easy.

Quite a list! But don't let it stress you out. Not every site / web-app must fulfill 100% of every item right away in the first version. And you might not agree with each item :)
I hope the list is useful as a checklist of things to consider, instead of being seen as a set of rules to be set in stone.