"It's not necessarily a contradiction. Trekkers communicating with each other would be likely to use the Vulcan hand salute even if they spoke Klingon to each other. It's not like the kid thought of himself as a Vulcan communicating with another Vulcan. He was a Star Trek fan communicating with a fellow Star Trek fan."
Exactly. If someone wants to get totally technical, they could say that "well, marvin was wearing a starfleet uniform when the kid spoke klingon to him and saluted with the vulcan hand signal." Big deal guys, he saw that there was a fellow Star Trek fan. I think the whole tribute to Star Trek was hilarious in this movie.
"The hideousness of that foot will haunt my dreams forever."

It's not necessarily a contradiction. Trekkers communicating with each other would be likely to use the Vulcan hand salute even if they spoke Klingon to each other. It's not like the kid thought of himself as a Vulcan communicating with another Vulcan. He was a Star Trek fan communicating with a fellow Star Trek fan.
I'm so uglythat's ok 'cause so are you.

You mean the Vulcan Salute, right?

Klingons and Vulcans are two totally different races/cultures in the Star Trek mythos. As a matter of fact, you could consider them polar opposites (Klingons=bloodthirsty warriors, Vulcans=logical pacifists).
A census taker once tried to test me. I ate his liver with some fava beans and a nice chiante.

This was one of this under rated film's charms. A surprising number of Star Trek references. I especially loved the puppet show of Wrath of Kahn. That made me laugh. And didn't Eddie Murphy spoof Star Wars in The Klumps movie (Nutty Prof. 2)??? He's got a history of doing stuff like that.
I rented this movie with low expectations, and it surprised me. Not a classic but one of Murphy's better recent flicks.

Sorry, I'm not a Star Trek Fan, but isn't the Klingon speaking and vulcan thing both from Star Trek? What makes them so odd being together?

Plus Marvin didn't do the sign right away, he just kind of did it with a little "yeah, whatever" look on his face. Look at his face again, and you'll see what I mean. Well, not "yeah, whatever", but kind of "okay, sure". I don't know! Just watch him next time and you'll see!
"
So, hiff ya screw it up, hi'm gonna hit ya hard, hi'm gonna hit ya fast!
" ~ Dr Cox

I'm not a Daddy Day Care fan it just seemed odd to me the first time I saw it. What you said makes sense though.

I'm not one to nit-pick, makes no difference to me. I'm sure it's just a bit of sloppy writing. But regardless, if a little kid did something deemed incorrect according to the fandom, it wouldn't be very nice to not return the gesture the only other alternatives would be to a) ignore the sign completely and risk upsetting him, or b) correct him and risk upsetting him.
Of course Marvin WAS quick to correct Flash's attempts to name villains
Well, that's enough of overanalyzing Daddy Day Care for me for one day. ^^