It should be pretty clear who we're referring to and when. The etymology of some of these nicknames may prove more elusive.
Lenny DiNardo (The Lenny) Oakland's sixth starter was much beloved in these parts and an entirely fictional ménage with stringbean hottie/hometown discount sucker Bronson Arroyo caught the imagination of the Comment Board community. Because of his gentle demeanour and good grooming it was assumed that Lenny would occupy the traditional female role in this affair. Accordingly, the submissive partner in any same-sex relationship might be pigeonholed as "The Lenny".
Kason Gabbard(Typo) On a QWERTY keyboard the "K" is immediately adjacent to the "J". His name is "Kason". We feel that this is more than a coincidence. By logical progression a fifth strikeout by the soft-throwing leftie might be celebrated with celebratory post of "JJJJJason!"
Mike Lowell (Scenic Lowell, Señor Doubles, BEA ARTHUR LOWELL!!(?!?!?)) He's easy on the eye, he's Puerto Rican, and he always gets to second base. Obvious, right? The last monicker's origins are rather more specific and obscure. Beth's mistaken assertion that Lowell's wife was named Beartha (actual name Bertica) provoked sporadic poster Don Penguino to speculate that Lowell might in fact be married to the gravel-voiced Golden Girls comedienne.
Dustin Pedroia (Munchkin Of Havoc, D2-P2) His swing and his capacity for turning a game on its head by sheer force of will are utterly disproportionate to his size (4' 11", 95lbs). His pluck, his usefulness, and his limited height remind certain folks of the ickle robot from Star Wars.
Wily Mo Pena (WMP451) Coined by Dover (?) after a monster blast at Kauffman estimated at 451 feet. (WMP90) Used very occasionally, after the big man gets a base on balls.
Julian Tavarez (Batshit) Jools somehow survived being associated with Rudy Seanez and eventually won our hearts with some sterling starting performances at the end of a miserable 2006. We heart him, because everything about him is erratic. In fact the dude is batshit insane.
Mike Timlin (Old Yeller) In the minds of certain posters his sudden propensity for allowing inherited runners to score was broadly equivalent to a beloved pet (see 2003 - 4) contracting rabies. A humane execution behind the woodshed was proposed. Also he's old and he yells a lot.
Please pop your corrections or suggestions in the comments, guys, and I'll edit accordingly.