Does vulgara hold the same negative connotations that the English vulgar has?
Example:

"Don't you dare use those vulgar words with me"

If not when would we use it over the root ordinara when discussing common place ideas?

Also does anyone have a word for 4WD, I can't for the life of me find an Esperanto construction that would describe a 4WD, and yes I know about ĵipo but that only means jeep.

From a CorpusEye search 'vulgara' seems to be used mainly in connection with languages and plants.

To express the idea of 'rude' Esperanto offers maldeca, maldelikata, triviala, familiara, malrafinita, kruda.

In French a 4x4 is a 'quatre-quatre' - which we could imitate in Esperanto as a 'Kvar-kvaro'.

Four wheel drive, technically, might be 4-rada transmisio, perhaps also 4-rada ruligo.

Vulgara =
1) ĝenerale, ordinare uzata,
2) triviala, maldelikata

In English:

1) generally, ordinarily used
2) commonplace, vulgar, coarse, harsh, crude

Compare the senses "vulgar Latin" with "vulgar slang".

So, a common place idea would be more "ordinara", where as a common phrase would be closer to "vulgara frazo".

I think at least

According to Wells vulgara means "common, everyday; vernacular". "Vulgar" is triviala, maldelikata, vulgaraĉa.

Thus, the Esperanto word is a falsa amiko, and you need the suffix aĉ (for undesirability) to convert it to a closer equivalent.

4WD is found in Wells too; it is kvar-rada transmisio.

See how useful Wells is! Perhaps you should consider investing in a copy, when circumstances permit.

Reta-vortara defino de Vulgara

As with the link above, Reta vortaro doesn't seem to mind giving "vulgara" the definition of "triviala/maldelikata" (mind you that is in context - which probably helps of course, out of context vulgaraĉa seems a bucket load more useful).

This doesn't seem quite so much a false friend with the English word, since in proper use in English, "vulgar" means the exact same. So rather than being a false friend, I think it's just that in Esperanto it's used properly more often, than in English.

After all, I don't believe you can describe horrid things as vulgar in English unless it's a thing associated with commoners or being common (e.g. sex, drugs, and rock and roll, as opposed to more extravagant examples like destroying the universe, things that can't be associated as being common to a group).

To extrapolate on that, a terrorist bombing can be a vulgar act, not because many do it, but in context because it's not exactly new for terrorists. We've seen/heard/had it before. Where as if it were a terrorist hamburger eating contest, it can still be vulgar, but that's because it's common to the middle/lower classes, who can't afford to dine at tables made of pure gold and eat the finest duck and caviar.

Of course, in "vulgar language", e.g. Vulgar Latin vs. a truly primitive and coarse language, then vulgara and vulgaraĉa need to be used in comparison. But otherwise I don't think that in normal speech, "vulgara" will be misinterpreted if they know what that means for the thing described. No one who pays attention to the news these days would misinterpret "la vulgara terorista bombado" as "la ĉiutaga ĉieesta terorista bombado", I hope.

I wouldn't regard the Reta Vortaro as authoritative as Wells, but even if we do, the usual meaning of "vulgar" and that of vulgara are different. I had shortened my message, but maybe I should have left the full explanation in!

Well, either way, just use "vulgar" for the 1st definition... I honesty couldn't care less about the second where there's a bazillion ways to phrase the damn thing