TeX

\catcode`\\=10

I'm not sure this will actually work, but in theory this should break \ as escape character leaving you no way to fix it. Normally TeX can read and write files, now it can't write anything that depends on logic. Thus the language is now broken as defined by OP.

EDIT: Other kill commands taken from the comments (although both might violate the code-must-be-executed rule):

• \def\fi{}\iffalse by smpl creates an un-closable if branch
• \catcode13=9% by iwillnotexist idonotexist creates a never-ending comment

TeX

\catcode`\\=10

I'm not sure this will actually work, but in theory this should break \ as escape character leaving you no way to fix it. Normally TeX can read and write files, now it can't write anything that depends on logic. Thus the language is now broken as defined by OP.

EDIT: Other kill commands taken from the comments (although both might violate the code-must-be-executed rule):

• \def\fi{}\iffalse by smpl creates an un-closable if branch
• \catcode13=9% by iwillnotexist idonotexist creates a never-ending comment

TeX

\catcode`\\=10

I'm not sure this will actually work, but in theory this should break \ as escape character leaving you no way to fix it. Normally TeX can read and write files, now it can't write anything that depends on logic.

EDIT: Other kill commands taken from the comments:

• \def\fi{}\iffalse by smpl creates an un-closable if branch
• \catcode13=9% by iwillnotexist idonotexist creates a never-ending comment

TeX

\catcode`\\=10

I'm not sure this will actually work, but in theory this should break \ as escape character leaving you no way to fix it. Normally TeX can read and write files, now it can't write anything that depends on logic. Thus the language is now broken as defined by OP.

EDIT: Other kill commands taken from the comments (although both might violate the code-must-be-executed rule):

• \def\fi{}\iffalse by smpl creates an un-closable if branch
• \catcode13=9% by iwillnotexist idonotexist creates a never-ending comment

TeX

\catcode`\\=10

I'm not sure this will actually work, but in theory this should break \ as escape character leaving you no way to fix it. Normally TeX can read and write files, now it can't write anything that depends on logic.

TeX

\catcode`\\=10

I'm not sure this will actually work, but in theory this should break \ as escape character leaving you no way to fix it. Normally TeX can read and write files, now it can't write anything that depends on logic.

EDIT: Other kill commands taken from the comments:

• \def\fi{}\iffalse by smpl creates an un-closable if branch
• \catcode13=9% by iwillnotexist idonotexist creates a never-ending comment