My friend plays Bb way too much

Any major triad is only present in 3 of the 12 keys.

Not quite... there are also minor keys.

Any major triad can appear as a natural harmonization in EIGHT keys.

To take that Bb chord (Bb-D-F), it appears in these scales:

Bb: Bb-C-D-E-F-G-A-Bb as the I
Eb: Eb-F-G-Ab-Bb-C-D-Eb as the V
F: F-G-A-Bb-C-D-E-F as the IV
G natural minor: G-A-Bb-C-D-Eb-F-G as the III
Eb harmonic (or melodic) minor: Eb-F-Gb-Ab-Bb-Cb (or C)-D-Eb as the V
D natural (or harmonic) minor: D-E-F-G-A-Bb-C (or C#)-D as the VI
F melodic minor: F-G-Ab-Bb-C-D-E-F as the IV
C natural minor: C-D-Eb-F-G-Ab-Bb-C as the VII

That's a major reason why it's so hard to tell what key a tune is in from just one or two chords.

Dennis, I think you are right.  He isn't wrong to play Bb, but he plays it way to often.

Use the same embellishment every time you play in a key and it ceases to be special.

Hey nick, question, on your user pic what exactly are you doing??

are you pulling something out of your ear?

He's obviously pulling a microphone out of his ear.

I only ever lip sync so I can place the microphone just about anywhere with the same effect.