My vote goes to saying Kegavno in Kaballas Shabbos, and not eating gebrokts on Pesach.

Davening mincha when it's dark outside. [I don't know if that's a minhag, but I'm substituting practice for minhag.]

I'm not sure that that counts, since there are some chassidusn which mellowed out and stopped doing that.

Really? Which ones?

That is not a "chassidic" minhag, it is following the opinion of Rabbienu Tam for when sunset is....

eat shlaosh seudos after shekiya,kegavna and i guess saying mizmor ledavid hashem royi loy echsor b4 aleinu after maariv friday night,saying hodu before mincha on erev shabbos - that was def. instituted by the besht,accepting upon urself the mitzcah of ahavta lerayecha before shacharis(minag ari but in all chassidish siddurs)
there are really hundreds - u just have to look thru the seforim and stuff
2 hole tzitzis became a universally accepted chassidish minhag and i think its orginally from the ari
diff opinions on eating raw onions on sabbos by day - some say yes and some say no - bRESLOV - SAYS nO TO RAw onions on shabbos

Is your punctuation hinting at some secret inyan?

No

You mean non-chasidim generally eat gebrokts??

I would vote for the daily mikvah dunk...

The recitation of the 23rd Psalm before 'Alenu on ereb Shabbath is not something unique to Hassidim. Sepharadim (Eastern and Western), Mizrahim, and Temanim all say it between the end of the 'amidah and 'alenu.

Wearing the same style glasses der alter rebbe wore, even though if he were still alive he'd be embaressed to be seen wearing them.