Just a questions ... messing with scales

Almost.

G is the fourth postion in the D major scale so it's a G Lydian scale. G Mixolidian would be a C scale (G, A, B, C, D, E, F, G) since G is the fifth position in C major.

Hope this helps.

Peace

im just a bit confused as to why a "c" would sound very bad against a G chord progression. which chord were you playing it over?

The perfect fourth (from G to C) is generally considered an avoid note or dissonant against the major chord but the #4 or #11 is more pleasing. But the fourth can be used effectively in solos - avoid is not my favorite way of describing it, maybe use with caution is better (ie. on weak/off beats).

The #4 is a tritone against a major chord's root and a b9* with the chord's fifth. Those are the two most dissonant intervals - so it is not considered pleasing to the average ear.

The perfect fourth is also a bit unnerving - because it's a b9 against the major third in a chord. As a general rule, if you use a fourth you want to resolve it immediately (more advanced improvisers can sit on it, but they know what it'll sound like in advance, so they're deliberately using the dissonance.)

In popular music and rock you'll see the fourth used a LOT - it's in the minor pentatonic scale, so it's the bread-and-butter choice. In blues you'll see both, but the #4 (or b5) is a 'blue note' - you'll resolve it pretty quickly, and you won't worry about the dissonance between the 4th and the chord's 3rd - that's characteristic of the blues.

That leaves jazz. A major scale with a #4 is the Lydian scale/mode, and it's used fairly often in major key jazz. The #11 is also used pretty often against a dominant chord, suggesting an extended/altered harmony. And in jazz, extended chords are used often, and the fifth is often excluded from the harmony that's being played when those chords are realized by the rhythm section. If you're soloing over a Cmaj9, it's very likely that the chord is voiced C-E-B-D (no G), and that eliminates one of the two dissonances, making it no more dissonant than a perfect fourth is in rock or blues.

Context is very important. Every style has its own idioms and vocabulary - musical and otherwise. I'm pretty sure wkriski is coming from a jazz perspective, because he used the term 'avoid note' - that's used a lot more often in jazz than other styles.

*I'm using the term b9 here because that's how it would be labeled when the melody note is analyzed as part of the chord structure. The actual interval could also be a b2.