[tigerlily]

There's also "proof by picture", in which you can hastily attempt to prove or disprove something by drawing a suitable diagram in your exam booklet. You have to be darn sure of what you're doing though... ;)

[tmhn2]

And another fun and powerful technique is "proof by intimidation" (https://en.wikipedia.org/wiki/Proof_by_intimidation), in which you don't have to know what you're doing, but other people have to think you do.

[constantcrying]

Ironically when rigorous proofs were invented by the greeks, Euclids "proof by picture" was no less rigorous than modern formal logic.