Quinault is right that you need to back off judging your dad...and be careful not to push him away.
However, if this were merely that he doesn't cross himself when required, or doesn't kneel at the right time, or even that he has tobacco in his mouth in church...it would be okay.
However, receiving the Eurcharist is a completely different thing. Forget about chewing gum before the Eurcharist, it's the after that has me concerned. I've been taught not to spit anything out of my mouth after I've had Holy Communion. We are not to chew gum, eat apples off the core (because you are going to throw out the core), eat a chicken drumstick, etc. No spitting, lest some of the Eucharist also gets expelled.
Chewing tobacco and spitting is hardly acceptable post receipt of the Eucharist - in my opinion.
Could you maybe provide him with a pamphlet discussing the do/don'ts in church. Again, something not aimed specifically towards him, but, just general information that would include this in it...take off hat, turn off cellphone, no spitting after receiving the Eucharist...
If you don't have one, and need one...let me know...I'll whip one out for you and you can print it.
To me respecting the Body of Christ is most important...