Systema

[Zaine]

systema's sensitivity drills reminds me of tai chi push hands, but you are allowed to do all types of dirty tricks like pull hair.

To be fair any system will allow this, including Tai Chi. There are no rules in a street fight.

[JusticeZero]

There is a difference, though, between something being "not prohibited" and being noted as accepted and encouraged. It is not prohibited to walk around outdoors in public in a pink and green polka-dotted hoop skirt with rubber duckies tied to the edges, but it it not a choice of clothing you will see in use.

[MadMartialArts]

Any true combat or battlefield martial art, in other words, one that is not a sport, not meant to be a sport, will allow "dirty tricks" because the goal is survival not scoring points. Dirty tricks are legitimately not allowed in sport competitions, but in real life, anything goes if your life or the life of someone you want to protect is threatened.