Stax, 601 584 574 564 553 539 bytes
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Run and debug it
It does at least attempt to use different strategies for different pieces.
I've still got some hope for a few sections, but here's an explanation of the approaches so far.
The general approach is to push a bunch of stuff on the stack.
Then join it all together and split it in thirds.
' just a space
`jaH1"jS3!`X compressed literal for "Hello, World!" assigned to the x register
`38dZl;i#D]|@Y@*` compressed literal for "It's showtime talk to the hand"
^ convert to upper case; it compresses better in lower case
n'"|SY Wrap the x register in quotes and save it in the y register
`=j("sx6c1 ob`^ compressed literal for "you have been terminated" in upper
."9 literal for '"9'
yrD register y (quoted hello world), reversed, first character dropped
"ck,@ " literal
"^h{ai{W>bJ,^T+NLDK(G$s@+"! crammed array [725, 101597559, 354, 45325875, 1115935, -65, -85335]
$"5a9+"|t concat as strings, then map '5' to 'a' and '9' to '+'
`='9%[mh++PxF!` compressed literal for " Take Circle Line to "
`~J@[E<`n compressed literal for "Paddington"; copy the one about the circle
`jj_kmZ5` compressed literal for "Wood Lane"
n7T copy " Take Circle Line to " and truncate last 7 characters
"alert'"x'' some literals and x register
`~lLKPq'III^) .tI:G8?uMolVwpnT&u#` compressed literal with commas in place of semi-colons
.,;|t replace with semi-colons, which aren't allowed in compressed literals
`/zOXzN`",data,{s:bits8[],`x\0_;}`cC,main(){`cC,puts(,address,s);` C,return(0);} ".,"|t
compressed literal for "foreign", followed by a string template
"Nm\{<\3VdH,FF:c~7&u!n"96|E carefully chosen string literal interpreted in base 96
"eawu":B encoded in custom base "eawu"
`dzJxVHC"`'{`pS7yzeENLM%_'` two compressed literals with a '{' in the middle
"(String[]a){System." literal
x6) last 6 characters of register x
"`");}}" literal with escaped uote
"0;pKll>r&.sSP}JLNL==(>eP>-2\6fc8|)4&.:,1jA66O{t0>GpALk4I{.iDM:Gr_50ga"
90|E literal of ascii characters decoded in base 90
"[+-><],.":B re-encoded with a custom base of brainfuck
72:/ split at position 72
~ push the right half to the input stack, effectively the beginning
" `yo| :after{content:`y H;e;P1;@/;W;o;/l;;o;Q/r;l;d;2;P0 ('&%:9]!~}|z2Vxwv-,POqponl$Hjihf|B@@>,=<M:9&7Y#VV2TSn.Oe*c;(I&%$#`"mCBA?zxxv*Pb8``qo42mZF.{Iy*@dD'<;_?!\}}|z2VxSSQ main(){puts("
big string template including y register a few times
y9( first 9 characters of y
Lr$ wrap all stacks in array and concatenate
3Mm split into 3 equal parts and print as lines
System.alert
is triggering \$\endgroup\$