I alllow nobody to get me off center.
One thing I've always read and heard about mantras is that your subconscious sucks up word associations like a vacuum and doesn't always interpret them right. So for that reason, I've heard, you always want to phrase a mantra in terms that are POSITIVE. Iow, "nobody" (contains a negative) and "push me off center" (contains "push" and "off center" which are a bit disturbing, perhaps negative to your pysche) -- and perhaps your subconscious could misinterpret these and in some way, instead give energy to the thought "nobody" and to the thought of being "off center..." -- as in, maybe possibly..."I'm a nobody, I'm off-center." (Because the subconscious isn't very reliably logical, just an active collector.)
So by this theory--instead, you'd serve yourself better to say it this way:
I am calm, strong, and centered...
This also keeps the meaning about YOU and your POSITIVE intention for yourself (not on external forces or other "bodies" coming at you from the outside). It empowers you, doesn't empower externals.
xo
Hops