Devilities will report you to Helios.

No, not unless someone in your party reports you . So as long as you are with a group of three friends, you should be okay to take out your anger on those confounded enemies. Just keep it within the party.

First, there is a difference between being reported and ultimately being banned, and while a GM is the only person who can definitively answer your question, they have stated before that they cannot/will not discuss the terms of actual bans with anyone other than the player involved--i.e., it is not likely that a GM is going to pop up and tell you for sure that yes/no being reported for cursing at monsters will get you banned.
All that having been said, there is nothing to STOP a player from reporting you for what they think is offensive--whether or not it was directed at them--and if you look at the actual form to report someone you will see that it actually says something to the effect of, "used foul language and did not stop when asked" (no mention of the language being directed at them, just that strong language was used and you didn't stop when they asked you to). If you're really worried about this, the easiest thing to do is a.) continue to play with your friends who you know are not offended, and b.) just don't use it around players that you don't know WON'T be offended. You make the choice of expressing your frustration by cursing at monsters, but it is just as easy to NOT use that kind of language publicly.

Yes, everyone does it, but it's still wrong. 99% of the time nothing will happen, but there's still that small chance someone will report you and the rules will back them up.

Compare it to downloading music or using an unprotected wi-fi.

"Use foul, abusive, or offensive language. If a swear word is filtered in-game in Spiral Knights, do not use it on the Spiral Knights forums."

Here's the link to the page

In response to Narfle.

Yes. In the end it all boils down to your judgement.

No because foul language is filtered. Do not bypass the filters though, because that will lead to a ban. I once bypassed the r word and I was immediately given a notice. Immediately.

The r word is never funny

EVER

If you use "normal" swear words that are filtered through the chat filter, you shouldn't have any problems. Now if you're like me and you like to make up different spellings and pronunciations for swears... Then you might have a problem.

Try sci-fi swearwords, like smeghead or gorram.

I don't think they ban for those. They can be shown on TV, at least.

You said so yourself, you've "learned new words from these guys". Nobody will get angry with you if you swear at inanimate objects unless you teach their kid a word they shouldn't know. Just know who you're with. Don't be a completly bad influence, and you'll never get punished for little things like swearing.