When you're walking/riding/driving so slow that you get aggraveted by the situation, so you say "I'm speeding like a plum!". Since plums can't speed at all the direct meaning is contrasted in a sarcasticdefinition, emphasized as going so slow, almost stopping.
(carrying Corey in the bike)
Corey: Hurry up Tim! We're late for the soccer game!
Tim: I can't! I'm doing the best I can but You're too heavy.. we are speeding like a plum!
Tom: Fuck my ass.
Kevin: OK.
(after just finishing)
Kevin: You dirty fuck Tom, you made me pull out a plum. Now I have to go wash your shit off of my dick.
Tom: Occupational hazard, you faggot.
The sexiest sexaphone the world has ever laid eyes on. A charming personality never to be forgotten. Comes along with the words tasneem and sexy ..obviously has a great sense of humour..too cute for words.. (really bigging herself up ryt now lol)