My first attempt at one of these was after listening to a radio four program, can't remember which - probably I'm Sorry I haven't a Clue, and they gave the first two lines for listeners to finish off.

An amateur gardener from Bude
Developed a cactus quite lewd (the beginning)

He went in to inspect 'em
tripped over and wrecked 'em,
and much foul language ensued. (my ending)

Yesterday I wrote this one:

A man on his hols in Peru
thought he'd found a sweet petting zoo.
But the hamsters inside
ended up fried
because in Peru that's what they do.

and this also on the subject of cactus:

Don't ever buy a cactus
with the aim of trying to attract us,
cactii are too sharp
while we don't mean to carp
a cactus won't positively impact us.

"Normal" service will resume in a few days. :)