If someone is speaking and just used a simile, can you say they are speaking metaphorically even though they are using a simile and not a metaphor? Ex: "I'll be all over you! I'll be like peanut butter on toast with you!" Can you say the above is metaphorical even though a simile is being used? Thanks
Every simile is a metaphor; however, not every metaphor is a simile.
Thus the answer is yes.
Technically speaking, no you can't. I simile says that something is similar but not the same. A simile in English uses "like" or "as" to express this. A metaphor says that one thing is another thing. In English this is expressed with the word "is."
Your example "I'll be all over you. I'll be like peanut butter on toast." confuses things because you're mixing a metaphor and a simile. The first sentence is an indirect metaphor and the second is a simile. If you want to be clear, omit the first sentence. But, if people can't understand your second sentence on it's own then it's a weak or confusing metaphor.
Here are some examples of similes:
My book sold like hotcakes at a lumberjack breakfast. Your love is like a Chinese finger puzzle. You're acting like a little girl. We need to play as a team. David Bowie was like the Picasso of the rock world.
Here are some example of metaphors:
You are the wind beneath my wings. Peter is the rock upon which I will build my church. Presentations are Kryptonite for many business leaders. Business is war. Time is money. You are a / an $%#! (This site has some good examples that also don't use "is." This site also has some great examples.)
Having said all this many people will say that in order to use a simile one must be thinking metaphorically or comparing unlike things to find similarities. In some cases, it's not so clear. In your example, I feel some will argue that it is a metaphor. The trouble is that people use the expression "Speaking metaphorically" or "figuratively speaking" when describing both similes and metaphors. A business English book I use describes a metaphor: "...is when you describe one thing in terms of another to create impact." That's not a very precise definition. The book uses the example, "We need to play as a team." Technically, that's a simile. We need to act as if. But as if is not the same as are as in "We are a team."
Let's look at two of my examples to make this more clear. "My book sold like..." Clearly, you can see that a book is not a pancake, even if I pour maple syrup on it and say it's "all natural." I'm making a comparison. In "Business is war." you are saying that the two are the same. One is another. We're not pretending. And people often operate from the truth "business is war," committing many crimes and being confused when people are upset or they are prosecuted. People who operate from the "business is war" metaphor cannot step outside of that and see it as a simile. For them it is the truth.
Just one more example. An actor is sometimes accused of being wooden or stiff or "just reading their lines." This actor is seeing the script and play in simile terms. A great actor will be acting from the viewpoint that the script and drama are real. The story is real life: we're not just acting in front of a camera. So, in real life you can see the results of simile vs. metaphor thinking.
George Lakoff talks about metaphors at length in many of his books, and in his breakout book "Metaphors We Live By." It's not an easy read but worth it.
EDIT: The following website is great and will help clear this up: http://knowgramming.com/metaphors/metaphor_and_simile_difference.htm (Many thanks to JEL for this suggestion.)