Remain curious and constantly confused.
Do not use 'to be' verbs when describing interests or skills.
Oh and most important. To do it all for fun not because you want to 'improve' yourself. The rest follows.
Alternatively, he could be following the advice of Korzybski, in Science and Sanity en.wikipedia.org/wiki/Alfred_Korzybski
It's very easy to slip but I've gotten better in time.
For example, you can't say: Lua is better than Python[2]
Instead you say: I prefer Lua to Python
Or perhaps you say: More projects that I rate highly use Lua over Python.
Or maybe: Lua scores more highly on common performance benchmarks than Python
[1] http://en.wikipedia.org/wiki/E-Prime
[2] Just an example; I'm not actually saying Lua is better than Python
E-prime removes all conjugations of "to be" from English. <-- Not sure if quoting "to be" as a noun counts. :)
To avoid that I prefer to say I know Z. I use X instead of I am a X user. I am most skilled in Y not a Y'er. I really like A. It is still hard to see A die but I don't need to defend every affront as if I was the one insulted. I allow only a few things to help define part of my identity. Doing this actively, also triggers to conscious how much I don't want to slip into tribalism or stagnation.
And by being ok with confusion it means I don't fear new things, by being confused it means I'm learning, by being curious I'll actively seek to put my self beyond my ability.
PG talks about exactly this point in Keep Your Identity Small [1].
It's also the reason you shouldn't talk about religion or politics at work or with the in-laws. For exactly the reason you mentioned: attacking Ruby will feel to the Rubyist like a personal attack.
Some skills/knowledge aren't fun to develop, yet it's worthwhile to keep learning them, so what you're saying sounds to me like it'd result in skipping some important things.